/* memcontrol.c - Memory Controller
 *
 * Copyright IBM Corporation, 2007
 * Author Balbir Singh <balbir@linux.vnet.ibm.com>
 *
 * Copyright 2007 OpenVZ SWsoft Inc
 * Author: Pavel Emelianov <xemul@openvz.org>
 *
 * Memory thresholds
 * Copyright (C) 2009 Nokia Corporation
 * Author: Kirill A. Shutemov
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 */

#include <linux/res_counter.h>
#include <linux/memcontrol.h>
#include <linux/cgroup.h>
#include <linux/mm.h>
#include <linux/hugetlb.h>
#include <linux/pagemap.h>
#include <linux/smp.h>
#include <linux/page-flags.h>
#include <linux/backing-dev.h>
#include <linux/bit_spinlock.h>
#include <linux/rcupdate.h>
#include <linux/limits.h>
#include <linux/export.h>
#include <linux/mutex.h>
#include <linux/rbtree.h>
#include <linux/slab.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/spinlock.h>
#include <linux/eventfd.h>
#include <linux/sort.h>
#include <linux/fs.h>
#include <linux/seq_file.h>
#include <linux/vmalloc.h>
#include <linux/mm_inline.h>
#include <linux/page_cgroup.h>
#include <linux/cpu.h>
#include <linux/oom.h>
#include "internal.h"
#include <net/sock.h>
#include <net/ip.h>
#include <net/tcp_memcontrol.h>

#include <asm/uaccess.h>

#include <trace/events/vmscan.h>

struct cgroup_subsys mem_cgroup_subsys __read_mostly;
#define MEM_CGROUP_RECLAIM_RETRIES      5
static struct mem_cgroup *root_mem_cgroup __read_mostly;

#ifdef CONFIG_MEMCG_SWAP
/* Turned on only when memory cgroup is enabled && really_do_swap_account = 1 */
int do_swap_account __read_mostly;

/* for remember boot option*/
#ifdef CONFIG_MEMCG_SWAP_ENABLED
static int really_do_swap_account __initdata = 1;
#else
static int really_do_swap_account __initdata = 0;
#endif

#else
#define do_swap_account         0
#endif


/*
 * Statistics for memory cgroup.
 */
enum mem_cgroup_stat_index {
        /*
         * For MEM_CONTAINER_TYPE_ALL, usage = pagecache + rss.
         */
        MEM_CGROUP_STAT_CACHE,     /* # of pages charged as cache */
        MEM_CGROUP_STAT_RSS,       /* # of pages charged as anon rss */
        MEM_CGROUP_STAT_FILE_MAPPED,  /* # of pages charged as file rss */
        MEM_CGROUP_STAT_SWAP, /* # of pages, swapped out */
        MEM_CGROUP_STAT_NSTATS,
};

static const char * const mem_cgroup_stat_names[] = {
        "cache",
        "rss",
        "mapped_file",
        "swap",
};

enum mem_cgroup_events_index {
        MEM_CGROUP_EVENTS_PGPGIN,       /* # of pages paged in */
        MEM_CGROUP_EVENTS_PGPGOUT,      /* # of pages paged out */
        MEM_CGROUP_EVENTS_PGFAULT,      /* # of page-faults */
        MEM_CGROUP_EVENTS_PGMAJFAULT,   /* # of major page-faults */
        MEM_CGROUP_EVENTS_NSTATS,
};

static const char * const mem_cgroup_events_names[] = {
        "pgpgin",
        "pgpgout",
        "pgfault",
        "pgmajfault",
};

/*
 * Per memcg event counter is incremented at every pagein/pageout. With THP,
 * it will be incremated by the number of pages. This counter is used for
 * for trigger some periodic events. This is straightforward and better
 * than using jiffies etc. to handle periodic memcg event.
 */
enum mem_cgroup_events_target {
        MEM_CGROUP_TARGET_THRESH,
        MEM_CGROUP_TARGET_SOFTLIMIT,
        MEM_CGROUP_TARGET_NUMAINFO,
        MEM_CGROUP_NTARGETS,
};
#define THRESHOLDS_EVENTS_TARGET 128
#define SOFTLIMIT_EVENTS_TARGET 1024
#define NUMAINFO_EVENTS_TARGET  1024

struct mem_cgroup_stat_cpu {
        long count[MEM_CGROUP_STAT_NSTATS];
        unsigned long events[MEM_CGROUP_EVENTS_NSTATS];
        unsigned long nr_page_events;
        unsigned long targets[MEM_CGROUP_NTARGETS];
};

struct mem_cgroup_reclaim_iter {
        /* css_id of the last scanned hierarchy member */
        int position;
        /* scan generation, increased every round-trip */
        unsigned int generation;
};

/*
 * per-zone information in memory controller.
 */
struct mem_cgroup_per_zone {
        struct lruvec           lruvec;
        unsigned long           lru_size[NR_LRU_LISTS];

        struct mem_cgroup_reclaim_iter reclaim_iter[DEF_PRIORITY + 1];

        struct rb_node          tree_node;      /* RB tree node */
        unsigned long long      usage_in_excess;/* Set to the value by which */
                                                /* the soft limit is exceeded*/
        bool                    on_tree;
        struct mem_cgroup       *memcg;         /* Back pointer, we cannot */
                                                /* use container_of        */
};

struct mem_cgroup_per_node {
        struct mem_cgroup_per_zone zoneinfo[MAX_NR_ZONES];
};

struct mem_cgroup_lru_info {
        struct mem_cgroup_per_node *nodeinfo[MAX_NUMNODES];
};

/*
 * Cgroups above their limits are maintained in a RB-Tree, independent of
 * their hierarchy representation
 */

struct mem_cgroup_tree_per_zone {
        struct rb_root rb_root;
        spinlock_t lock;
};

struct mem_cgroup_tree_per_node {
        struct mem_cgroup_tree_per_zone rb_tree_per_zone[MAX_NR_ZONES];
};

struct mem_cgroup_tree {
        struct mem_cgroup_tree_per_node *rb_tree_per_node[MAX_NUMNODES];
};

static struct mem_cgroup_tree soft_limit_tree __read_mostly;

struct mem_cgroup_threshold {
        struct eventfd_ctx *eventfd;
        u64 threshold;
};

/* For threshold */
struct mem_cgroup_threshold_ary {
        /* An array index points to threshold just below or equal to usage. */
        int current_threshold;
        /* Size of entries[] */
        unsigned int size;
        /* Array of thresholds */
        struct mem_cgroup_threshold entries[0];
};

struct mem_cgroup_thresholds {
        /* Primary thresholds array */
        struct mem_cgroup_threshold_ary *primary;
        /*
         * Spare threshold array.
         * This is needed to make mem_cgroup_unregister_event() "never fail".
         * It must be able to store at least primary->size - 1 entries.
         */
        struct mem_cgroup_threshold_ary *spare;
};

/* for OOM */
struct mem_cgroup_eventfd_list {
        struct list_head list;
        struct eventfd_ctx *eventfd;
};

static void mem_cgroup_threshold(struct mem_cgroup *memcg);
static void mem_cgroup_oom_notify(struct mem_cgroup *memcg);

/*
 * The memory controller data structure. The memory controller controls both
 * page cache and RSS per cgroup. We would eventually like to provide
 * statistics based on the statistics developed by Rik Van Riel for clock-pro,
 * to help the administrator determine what knobs to tune.
 *
 * TODO: Add a water mark for the memory controller. Reclaim will begin when
 * we hit the water mark. May be even add a low water mark, such that
 * no reclaim occurs from a cgroup at it's low water mark, this is
 * a feature that will be implemented much later in the future.
 */
struct mem_cgroup {
        struct cgroup_subsys_state css;
        /*
         * the counter to account for memory usage
         */
        struct res_counter res;

        union {
                /*
                 * the counter to account for mem+swap usage.
                 */
                struct res_counter memsw;

                /*
                 * rcu_freeing is used only when freeing struct mem_cgroup,
                 * so put it into a union to avoid wasting more memory.
                 * It must be disjoint from the css field.  It could be
                 * in a union with the res field, but res plays a much
                 * larger part in mem_cgroup life than memsw, and might
                 * be of interest, even at time of free, when debugging.
                 * So share rcu_head with the less interesting memsw.
                 */
                struct rcu_head rcu_freeing;
                /*
                 * We also need some space for a worker in deferred freeing.
                 * By the time we call it, rcu_freeing is no longer in use.
                 */
                struct work_struct work_freeing;
        };

        /*
         * Per cgroup active and inactive list, similar to the
         * per zone LRU lists.
         */
        struct mem_cgroup_lru_info info;
        int last_scanned_node;
#if MAX_NUMNODES > 1
        nodemask_t      scan_nodes;
        atomic_t        numainfo_events;
        atomic_t        numainfo_updating;
#endif
        /*
         * Should the accounting and control be hierarchical, per subtree?
         */
        bool use_hierarchy;

        bool            oom_lock;
        atomic_t        under_oom;

        atomic_t        refcnt;

        int     swappiness;
        /* OOM-Killer disable */
        int             oom_kill_disable;

        /* set when res.limit == memsw.limit */
        bool            memsw_is_minimum;

        /* protect arrays of thresholds */
        struct mutex thresholds_lock;

        /* thresholds for memory usage. RCU-protected */
        struct mem_cgroup_thresholds thresholds;

        /* thresholds for mem+swap usage. RCU-protected */
        struct mem_cgroup_thresholds memsw_thresholds;

        /* For oom notifier event fd */
        struct list_head oom_notify;

        /*
         * Should we move charges of a task when a task is moved into this
         * mem_cgroup ? And what type of charges should we move ?
         */
        unsigned long   move_charge_at_immigrate;
        /*
         * set > 0 if pages under this cgroup are moving to other cgroup.
         */
        atomic_t        moving_account;
        /* taken only while moving_account > 0 */
        spinlock_t      move_lock;
        /*
         * percpu counter.
         */
        struct mem_cgroup_stat_cpu __percpu *stat;
        /*
         * used when a cpu is offlined or other synchronizations
         * See mem_cgroup_read_stat().
         */
        struct mem_cgroup_stat_cpu nocpu_base;
        spinlock_t pcp_counter_lock;

#if defined(CONFIG_MEMCG_KMEM) && defined(CONFIG_INET)
        struct tcp_memcontrol tcp_mem;
#endif
};

/* Stuffs for move charges at task migration. */
/*
 * Types of charges to be moved. "move_charge_at_immitgrate" is treated as a
 * left-shifted bitmap of these types.
 */
enum move_type {
        MOVE_CHARGE_TYPE_ANON,  /* private anonymous page and swap of it */
        MOVE_CHARGE_TYPE_FILE,  /* file page(including tmpfs) and swap of it */
        NR_MOVE_TYPE,
};

/* "mc" and its members are protected by cgroup_mutex */
static struct move_charge_struct {
        spinlock_t        lock; /* for from, to */
        struct mem_cgroup *from;
        struct mem_cgroup *to;
        unsigned long precharge;
        unsigned long moved_charge;
        unsigned long moved_swap;
        struct task_struct *moving_task;        /* a task moving charges */
        wait_queue_head_t waitq;                /* a waitq for other context */
} mc = {
        .lock = __SPIN_LOCK_UNLOCKED(mc.lock),
        .waitq = __WAIT_QUEUE_HEAD_INITIALIZER(mc.waitq),
};

static bool move_anon(void)
{
        return test_bit(MOVE_CHARGE_TYPE_ANON,
                                        &mc.to->move_charge_at_immigrate);
}

static bool move_file(void)
{
        return test_bit(MOVE_CHARGE_TYPE_FILE,
                                        &mc.to->move_charge_at_immigrate);
}

/*
 * Maximum loops in mem_cgroup_hierarchical_reclaim(), used for soft
 * limit reclaim to prevent infinite loops, if they ever occur.
 */
#define MEM_CGROUP_MAX_RECLAIM_LOOPS            100
#define MEM_CGROUP_MAX_SOFT_LIMIT_RECLAIM_LOOPS 2

enum charge_type {
        MEM_CGROUP_CHARGE_TYPE_CACHE = 0,
        MEM_CGROUP_CHARGE_TYPE_ANON,
        MEM_CGROUP_CHARGE_TYPE_SWAPOUT, /* for accounting swapcache */
        MEM_CGROUP_CHARGE_TYPE_DROP,    /* a page was unused swap cache */
        NR_CHARGE_TYPE,
};

/* for encoding cft->private value on file */
#define _MEM                    (0)
#define _MEMSWAP                (1)
#define _OOM_TYPE               (2)
#define MEMFILE_PRIVATE(x, val) ((x) << 16 | (val))
#define MEMFILE_TYPE(val)       ((val) >> 16 & 0xffff)
#define MEMFILE_ATTR(val)       ((val) & 0xffff)
/* Used for OOM nofiier */
#define OOM_CONTROL             (0)

/*
 * Reclaim flags for mem_cgroup_hierarchical_reclaim
 */
#define MEM_CGROUP_RECLAIM_NOSWAP_BIT   0x0
#define MEM_CGROUP_RECLAIM_NOSWAP       (1 << MEM_CGROUP_RECLAIM_NOSWAP_BIT)
#define MEM_CGROUP_RECLAIM_SHRINK_BIT   0x1
#define MEM_CGROUP_RECLAIM_SHRINK       (1 << MEM_CGROUP_RECLAIM_SHRINK_BIT)

static void mem_cgroup_get(struct mem_cgroup *memcg);
static void mem_cgroup_put(struct mem_cgroup *memcg);

static inline
struct mem_cgroup *mem_cgroup_from_css(struct cgroup_subsys_state *s)
{
        return container_of(s, struct mem_cgroup, css);
}

static inline bool mem_cgroup_is_root(struct mem_cgroup *memcg)
{
        return (memcg == root_mem_cgroup);
}

/* Writing them here to avoid exposing memcg's inner layout */
#if defined(CONFIG_INET) && defined(CONFIG_MEMCG_KMEM)

void sock_update_memcg(struct sock *sk)
{
        if (mem_cgroup_sockets_enabled) {
                struct mem_cgroup *memcg;
                struct cg_proto *cg_proto;

                BUG_ON(!sk->sk_prot->proto_cgroup);

                /* Socket cloning can throw us here with sk_cgrp already
                 * filled. It won't however, necessarily happen from
                 * process context. So the test for root memcg given
                 * the current task's memcg won't help us in this case.
                 *
                 * Respecting the original socket's memcg is a better
                 * decision in this case.
                 */
                if (sk->sk_cgrp) {
                        BUG_ON(mem_cgroup_is_root(sk->sk_cgrp->memcg));
                        mem_cgroup_get(sk->sk_cgrp->memcg);
                        return;
                }

                rcu_read_lock();
                memcg = mem_cgroup_from_task(current);
                cg_proto = sk->sk_prot->proto_cgroup(memcg);
                if (!mem_cgroup_is_root(memcg) && memcg_proto_active(cg_proto)) {
                        mem_cgroup_get(memcg);
                        sk->sk_cgrp = cg_proto;
                }
                rcu_read_unlock();
        }
}
EXPORT_SYMBOL(sock_update_memcg);

void sock_release_memcg(struct sock *sk)
{
        if (mem_cgroup_sockets_enabled && sk->sk_cgrp) {
                struct mem_cgroup *memcg;
                WARN_ON(!sk->sk_cgrp->memcg);
                memcg = sk->sk_cgrp->memcg;
                mem_cgroup_put(memcg);
        }
}

struct cg_proto *tcp_proto_cgroup(struct mem_cgroup *memcg)
{
        if (!memcg || mem_cgroup_is_root(memcg))
                return NULL;

        return &memcg->tcp_mem.cg_proto;
}
EXPORT_SYMBOL(tcp_proto_cgroup);

static void disarm_sock_keys(struct mem_cgroup *memcg)
{
        if (!memcg_proto_activated(&memcg->tcp_mem.cg_proto))
                return;
        static_key_slow_dec(&memcg_socket_limit_enabled);
}
#else
static void disarm_sock_keys(struct mem_cgroup *memcg)
{
}
#endif

static void drain_all_stock_async(struct mem_cgroup *memcg);

static struct mem_cgroup_per_zone *
mem_cgroup_zoneinfo(struct mem_cgroup *memcg, int nid, int zid)
{
        return &memcg->info.nodeinfo[nid]->zoneinfo[zid];
}

struct cgroup_subsys_state *mem_cgroup_css(struct mem_cgroup *memcg)
{
        return &memcg->css;
}

static struct mem_cgroup_per_zone *
page_cgroup_zoneinfo(struct mem_cgroup *memcg, struct page *page)
{
        int nid = page_to_nid(page);
        int zid = page_zonenum(page);

        return mem_cgroup_zoneinfo(memcg, nid, zid);
}

static struct mem_cgroup_tree_per_zone *
soft_limit_tree_node_zone(int nid, int zid)
{
        return &soft_limit_tree.rb_tree_per_node[nid]->rb_tree_per_zone[zid];
}

static struct mem_cgroup_tree_per_zone *
soft_limit_tree_from_page(struct page *page)
{
        int nid = page_to_nid(page);
        int zid = page_zonenum(page);

        return &soft_limit_tree.rb_tree_per_node[nid]->rb_tree_per_zone[zid];
}

static void
__mem_cgroup_insert_exceeded(struct mem_cgroup *memcg,
                                struct mem_cgroup_per_zone *mz,
                                struct mem_cgroup_tree_per_zone *mctz,
                                unsigned long long new_usage_in_excess)
{
        struct rb_node **p = &mctz->rb_root.rb_node;
        struct rb_node *parent = NULL;
        struct mem_cgroup_per_zone *mz_node;

        if (mz->on_tree)
                return;

        mz->usage_in_excess = new_usage_in_excess;
        if (!mz->usage_in_excess)
                return;
        while (*p) {
                parent = *p;
                mz_node = rb_entry(parent, struct mem_cgroup_per_zone,
                                        tree_node);
                if (mz->usage_in_excess < mz_node->usage_in_excess)
                        p = &(*p)->rb_left;
                /*
                 * We can't avoid mem cgroups that are over their soft
                 * limit by the same amount
                 */
                else if (mz->usage_in_excess >= mz_node->usage_in_excess)
                        p = &(*p)->rb_right;
        }
        rb_link_node(&mz->tree_node, parent, p);
        rb_insert_color(&mz->tree_node, &mctz->rb_root);
        mz->on_tree = true;
}

static void
__mem_cgroup_remove_exceeded(struct mem_cgroup *memcg,
                                struct mem_cgroup_per_zone *mz,
                                struct mem_cgroup_tree_per_zone *mctz)
{
        if (!mz->on_tree)
                return;
        rb_erase(&mz->tree_node, &mctz->rb_root);
        mz->on_tree = false;
}

static void
mem_cgroup_remove_exceeded(struct mem_cgroup *memcg,
                                struct mem_cgroup_per_zone *mz,
                                struct mem_cgroup_tree_per_zone *mctz)
{
        spin_lock(&mctz->lock);
        __mem_cgroup_remove_exceeded(memcg, mz, mctz);
        spin_unlock(&mctz->lock);
}


static void mem_cgroup_update_tree(struct mem_cgroup *memcg, struct page *page)
{
        unsigned long long excess;
        struct mem_cgroup_per_zone *mz;
        struct mem_cgroup_tree_per_zone *mctz;
        int nid = page_to_nid(page);
        int zid = page_zonenum(page);
        mctz = soft_limit_tree_from_page(page);

        /*
         * Necessary to update all ancestors when hierarchy is used.
         * because their event counter is not touched.
         */
        for (; memcg; memcg = parent_mem_cgroup(memcg)) {
                mz = mem_cgroup_zoneinfo(memcg, nid, zid);
                excess = res_counter_soft_limit_excess(&memcg->res);
                /*
                 * We have to update the tree if mz is on RB-tree or
                 * mem is over its softlimit.
                 */
                if (excess || mz->on_tree) {
                        spin_lock(&mctz->lock);
                        /* if on-tree, remove it */
                        if (mz->on_tree)
                                __mem_cgroup_remove_exceeded(memcg, mz, mctz);
                        /*
                         * Insert again. mz->usage_in_excess will be updated.
                         * If excess is 0, no tree ops.
                         */
                        __mem_cgroup_insert_exceeded(memcg, mz, mctz, excess);
                        spin_unlock(&mctz->lock);
                }
        }
}

static void mem_cgroup_remove_from_trees(struct mem_cgroup *memcg)
{
        int node, zone;
        struct mem_cgroup_per_zone *mz;
        struct mem_cgroup_tree_per_zone *mctz;

        for_each_node(node) {
                for (zone = 0; zone < MAX_NR_ZONES; zone++) {
                        mz = mem_cgroup_zoneinfo(memcg, node, zone);
                        mctz = soft_limit_tree_node_zone(node, zone);
                        mem_cgroup_remove_exceeded(memcg, mz, mctz);
                }
        }
}

static struct mem_cgroup_per_zone *
__mem_cgroup_largest_soft_limit_node(struct mem_cgroup_tree_per_zone *mctz)
{
        struct rb_node *rightmost = NULL;
        struct mem_cgroup_per_zone *mz;

retry:
        mz = NULL;
        rightmost = rb_last(&mctz->rb_root);
        if (!rightmost)
                goto done;              /* Nothing to reclaim from */

        mz = rb_entry(rightmost, struct mem_cgroup_per_zone, tree_node);
        /*
         * Remove the node now but someone else can add it back,
         * we will to add it back at the end of reclaim to its correct
         * position in the tree.
         */
        __mem_cgroup_remove_exceeded(mz->memcg, mz, mctz);
        if (!res_counter_soft_limit_excess(&mz->memcg->res) ||
                !css_tryget(&mz->memcg->css))
                goto retry;
done:
        return mz;
}

static struct mem_cgroup_per_zone *
mem_cgroup_largest_soft_limit_node(struct mem_cgroup_tree_per_zone *mctz)
{
        struct mem_cgroup_per_zone *mz;

        spin_lock(&mctz->lock);
        mz = __mem_cgroup_largest_soft_limit_node(mctz);
        spin_unlock(&mctz->lock);
        return mz;
}

/*
 * Implementation Note: reading percpu statistics for memcg.
 *
 * Both of vmstat[] and percpu_counter has threshold and do periodic
 * synchronization to implement "quick" read. There are trade-off between
 * reading cost and precision of value. Then, we may have a chance to implement
 * a periodic synchronizion of counter in memcg's counter.
 *
 * But this _read() function is used for user interface now. The user accounts
 * memory usage by memory cgroup and he _always_ requires exact value because
 * he accounts memory. Even if we provide quick-and-fuzzy read, we always
 * have to visit all online cpus and make sum. So, for now, unnecessary
 * synchronization is not implemented. (just implemented for cpu hotplug)
 *
 * If there are kernel internal actions which can make use of some not-exact
 * value, and reading all cpu value can be performance bottleneck in some
 * common workload, threashold and synchonization as vmstat[] should be
 * implemented.
 */
static long mem_cgroup_read_stat(struct mem_cgroup *memcg,
                                 enum mem_cgroup_stat_index idx)
{
        long val = 0;
        int cpu;

        get_online_cpus();
        for_each_online_cpu(cpu)
                val += per_cpu(memcg->stat->count[idx], cpu);
#ifdef CONFIG_HOTPLUG_CPU
        spin_lock(&memcg->pcp_counter_lock);
        val += memcg->nocpu_base.count[idx];
        spin_unlock(&memcg->pcp_counter_lock);
#endif
        put_online_cpus();
        return val;
}

static void mem_cgroup_swap_statistics(struct mem_cgroup *memcg,
                                         bool charge)
{
        int val = (charge) ? 1 : -1;
        this_cpu_add(memcg->stat->count[MEM_CGROUP_STAT_SWAP], val);
}

static unsigned long mem_cgroup_read_events(struct mem_cgroup *memcg,
                                            enum mem_cgroup_events_index idx)
{
        unsigned long val = 0;
        int cpu;

        for_each_online_cpu(cpu)
                val += per_cpu(memcg->stat->events[idx], cpu);
#ifdef CONFIG_HOTPLUG_CPU
        spin_lock(&memcg->pcp_counter_lock);
        val += memcg->nocpu_base.events[idx];
        spin_unlock(&memcg->pcp_counter_lock);
#endif
        return val;
}

static void mem_cgroup_charge_statistics(struct mem_cgroup *memcg,
                                         bool anon, int nr_pages)
{
        preempt_disable();

        /*
         * Here, RSS means 'mapped anon' and anon's SwapCache. Shmem/tmpfs is
         * counted as CACHE even if it's on ANON LRU.
         */
        if (anon)
                __this_cpu_add(memcg->stat->count[MEM_CGROUP_STAT_RSS],
                                nr_pages);
        else
                __this_cpu_add(memcg->stat->count[MEM_CGROUP_STAT_CACHE],
                                nr_pages);

        /* pagein of a big page is an event. So, ignore page size */
        if (nr_pages > 0)
                __this_cpu_inc(memcg->stat->events[MEM_CGROUP_EVENTS_PGPGIN]);
        else {
                __this_cpu_inc(memcg->stat->events[MEM_CGROUP_EVENTS_PGPGOUT]);
                nr_pages = -nr_pages; /* for event */
        }

        __this_cpu_add(memcg->stat->nr_page_events, nr_pages);

        preempt_enable();
}

unsigned long
mem_cgroup_get_lru_size(struct lruvec *lruvec, enum lru_list lru)
{
        struct mem_cgroup_per_zone *mz;

        mz = container_of(lruvec, struct mem_cgroup_per_zone, lruvec);
        return mz->lru_size[lru];
}

static unsigned long
mem_cgroup_zone_nr_lru_pages(struct mem_cgroup *memcg, int nid, int zid,
                        unsigned int lru_mask)
{
        struct mem_cgroup_per_zone *mz;
        enum lru_list lru;
        unsigned long ret = 0;

        mz = mem_cgroup_zoneinfo(memcg, nid, zid);

        for_each_lru(lru) {
                if (BIT(lru) & lru_mask)
                        ret += mz->lru_size[lru];
        }
        return ret;
}

static unsigned long
mem_cgroup_node_nr_lru_pages(struct mem_cgroup *memcg,
                        int nid, unsigned int lru_mask)
{
        u64 total = 0;
        int zid;

        for (zid = 0; zid < MAX_NR_ZONES; zid++)
                total += mem_cgroup_zone_nr_lru_pages(memcg,
                                                nid, zid, lru_mask);

        return total;
}

static unsigned long mem_cgroup_nr_lru_pages(struct mem_cgroup *memcg,
                        unsigned int lru_mask)
{
        int nid;
        u64 total = 0;

        for_each_node_state(nid, N_HIGH_MEMORY)
                total += mem_cgroup_node_nr_lru_pages(memcg, nid, lru_mask);
        return total;
}

static bool mem_cgroup_event_ratelimit(struct mem_cgroup *memcg,
                                       enum mem_cgroup_events_target target)
{
        unsigned long val, next;

        val = __this_cpu_read(memcg->stat->nr_page_events);
        next = __this_cpu_read(memcg->stat->targets[target]);
        /* from time_after() in jiffies.h */
        if ((long)next - (long)val < 0) {
                switch (target) {
                case MEM_CGROUP_TARGET_THRESH:
                        next = val + THRESHOLDS_EVENTS_TARGET;
                        break;
                case MEM_CGROUP_TARGET_SOFTLIMIT:
                        next = val + SOFTLIMIT_EVENTS_TARGET;
                        break;
                case MEM_CGROUP_TARGET_NUMAINFO:
                        next = val + NUMAINFO_EVENTS_TARGET;
                        break;
                default:
                        break;
                }
                __this_cpu_write(memcg->stat->targets[target], next);
                return true;
        }
        return false;
}

/*
 * Check events in order.
 *
 */
static void memcg_check_events(struct mem_cgroup *memcg, struct page *page)
{
        preempt_disable();
        /* threshold event is triggered in finer grain than soft limit */
        if (unlikely(mem_cgroup_event_ratelimit(memcg,
                                                MEM_CGROUP_TARGET_THRESH))) {
                bool do_softlimit;
                bool do_numainfo __maybe_unused;

                do_softlimit = mem_cgroup_event_ratelimit(memcg,
                                                MEM_CGROUP_TARGET_SOFTLIMIT);
#if MAX_NUMNODES > 1
                do_numainfo = mem_cgroup_event_ratelimit(memcg,
                                                MEM_CGROUP_TARGET_NUMAINFO);
#endif
                preempt_enable();

                mem_cgroup_threshold(memcg);
                if (unlikely(do_softlimit))
                        mem_cgroup_update_tree(memcg, page);
#if MAX_NUMNODES > 1
                if (unlikely(do_numainfo))
                        atomic_inc(&memcg->numainfo_events);
#endif
        } else
                preempt_enable();
}

struct mem_cgroup *mem_cgroup_from_cont(struct cgroup *cont)
{
        return mem_cgroup_from_css(
                cgroup_subsys_state(cont, mem_cgroup_subsys_id));
}

struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p)
{
        /*
         * mm_update_next_owner() may clear mm->owner to NULL
         * if it races with swapoff, page migration, etc.
         * So this can be called with p == NULL.
         */
        if (unlikely(!p))
                return NULL;

        return mem_cgroup_from_css(task_subsys_state(p, mem_cgroup_subsys_id));
}

struct mem_cgroup *try_get_mem_cgroup_from_mm(struct mm_struct *mm)
{
        struct mem_cgroup *memcg = NULL;

        if (!mm)
                return NULL;
        /*
         * Because we have no locks, mm->owner's may be being moved to other
         * cgroup. We use css_tryget() here even if this looks
         * pessimistic (rather than adding locks here).
         */
        rcu_read_lock();
        do {
                memcg = mem_cgroup_from_task(rcu_dereference(mm->owner));
                if (unlikely(!memcg))
                        break;
        } while (!css_tryget(&memcg->css));
        rcu_read_unlock();
        return memcg;
}

/**
 * mem_cgroup_iter - iterate over memory cgroup hierarchy
 * @root: hierarchy root
 * @prev: previously returned memcg, NULL on first invocation
 * @reclaim: cookie for shared reclaim walks, NULL for full walks
 *
 * Returns references to children of the hierarchy below @root, or
 * @root itself, or %NULL after a full round-trip.
 *
 * Caller must pass the return value in @prev on subsequent
 * invocations for reference counting, or use mem_cgroup_iter_break()
 * to cancel a hierarchy walk before the round-trip is complete.
 *
 * Reclaimers can specify a zone and a priority level in @reclaim to
 * divide up the memcgs in the hierarchy among all concurrent
 * reclaimers operating on the same zone and priority.
 */
struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
                                   struct mem_cgroup *prev,
                                   struct mem_cgroup_reclaim_cookie *reclaim)
{
        struct mem_cgroup *memcg = NULL;
        int id = 0;

        if (mem_cgroup_disabled())
                return NULL;

        if (!root)
                root = root_mem_cgroup;

        if (prev && !reclaim)
                id = css_id(&prev->css);

        if (prev && prev != root)
                css_put(&prev->css);

        if (!root->use_hierarchy && root != root_mem_cgroup) {
                if (prev)
                        return NULL;
                return root;
        }

        while (!memcg) {
                struct mem_cgroup_reclaim_iter *uninitialized_var(iter);
                struct cgroup_subsys_state *css;

                if (reclaim) {
                        int nid = zone_to_nid(reclaim->zone);
                        int zid = zone_idx(reclaim->zone);
                        struct mem_cgroup_per_zone *mz;

                        mz = mem_cgroup_zoneinfo(root, nid, zid);
                        iter = &mz->reclaim_iter[reclaim->priority];
                        if (prev && reclaim->generation != iter->generation)
                                return NULL;
                        id = iter->position;
                }

                rcu_read_lock();
                css = css_get_next(&mem_cgroup_subsys, id + 1, &root->css, &id);
                if (css) {
                        if (css == &root->css || css_tryget(css))
                                memcg = mem_cgroup_from_css(css);
                } else
                        id = 0;
                rcu_read_unlock();

                if (reclaim) {
                        iter->position = id;
                        if (!css)
                                iter->generation++;
                        else if (!prev && memcg)
                                reclaim->generation = iter->generation;
                }

                if (prev && !css)
                        return NULL;
        }
        return memcg;
}

/**
 * mem_cgroup_iter_break - abort a hierarchy walk prematurely
 * @root: hierarchy root
 * @prev: last visited hierarchy member as returned by mem_cgroup_iter()
 */
void mem_cgroup_iter_break(struct mem_cgroup *root,
                           struct mem_cgroup *prev)
{
        if (!root)
                root = root_mem_cgroup;
        if (prev && prev != root)
                css_put(&prev->css);

}

/*
 * Iteration constructs for visiting all cgroups (under a tree).  If
 * loops are exited prematurely (break), mem_cgroup_iter_break() must
 * be used for reference counting.
 */
#define for_each_mem_cgroup_tree(iter, root)            \
        for (iter = mem_cgroup_iter(root, NULL, NULL);  \
             iter != NULL;                              \
             iter = mem_cgroup_iter(root, iter, NULL))

#define for_each_mem_cgroup(iter)                       \
        for (iter = mem_cgroup_iter(NULL, NULL, NULL);  \
             iter != NULL;                              \
             iter = mem_cgroup_iter(NULL, iter, NULL))

void mem_cgroup_count_vm_event(struct mm_struct *mm, enum vm_event_item idx)
{
        struct mem_cgroup *memcg;

        if (!mm)
                return;

        rcu_read_lock();
        memcg = mem_cgroup_from_task(rcu_dereference(mm->owner));
        if (unlikely(!memcg))
                goto out;

        switch (idx) {
        case PGFAULT:
                this_cpu_inc(memcg->stat->events[MEM_CGROUP_EVENTS_PGFAULT]);
                break;
        case PGMAJFAULT:
                this_cpu_inc(memcg->stat->events[MEM_CGROUP_EVENTS_PGMAJFAULT]);
                break;
        default:
                BUG();
        }
out:
        rcu_read_unlock();
}
EXPORT_SYMBOL(mem_cgroup_count_vm_event);

/**
 * mem_cgroup_zone_lruvec - get the lru list vector for a zone and memcg
 * @zone: zone of the wanted lruvec
 * @memcg: memcg of the wanted lruvec
 *
 * Returns the lru list vector holding pages for the given @zone and
 * @mem.  This can be the global zone lruvec, if the memory controller
 * is disabled.
 */
struct lruvec *mem_cgroup_zone_lruvec(struct zone *zone,
                                      struct mem_cgroup *memcg)
{
        struct mem_cgroup_per_zone *mz;
        struct lruvec *lruvec;

        if (mem_cgroup_disabled()) {
                lruvec = &zone->lruvec;
                goto out;
        }

        mz = mem_cgroup_zoneinfo(memcg, zone_to_nid(zone), zone_idx(zone));
        lruvec = &mz->lruvec;
out:
        /*
         * Since a node can be onlined after the mem_cgroup was created,
         * we have to be prepared to initialize lruvec->zone here;
         * and if offlined then reonlined, we need to reinitialize it.
         */
        if (unlikely(lruvec->zone != zone))
                lruvec->zone = zone;
        return lruvec;
}

/*
 * Following LRU functions are allowed to be used without PCG_LOCK.
 * Operations are called by routine of global LRU independently from memcg.
 * What we have to take care of here is validness of pc->mem_cgroup.
 *
 * Changes to pc->mem_cgroup happens when
 * 1. charge
 * 2. moving account
 * In typical case, "charge" is done before add-to-lru. Exception is SwapCache.
 * It is added to LRU before charge.
 * If PCG_USED bit is not set, page_cgroup is not added to this private LRU.
 * When moving account, the page is not on LRU. It's isolated.
 */

/**
 * mem_cgroup_page_lruvec - return lruvec for adding an lru page
 * @page: the page
 * @zone: zone of the page
 */
struct lruvec *mem_cgroup_page_lruvec(struct page *page, struct zone *zone)
{
        struct mem_cgroup_per_zone *mz;
        struct mem_cgroup *memcg;
        struct page_cgroup *pc;
        struct lruvec *lruvec;

        if (mem_cgroup_disabled()) {
                lruvec = &zone->lruvec;
                goto out;
        }

        pc = lookup_page_cgroup(page);
        memcg = pc->mem_cgroup;

        /*
         * Surreptitiously switch any uncharged offlist page to root:
         * an uncharged page off lru does nothing to secure
         * its former mem_cgroup from sudden removal.
         *
         * Our caller holds lru_lock, and PageCgroupUsed is updated
         * under page_cgroup lock: between them, they make all uses
         * of pc->mem_cgroup safe.
         */
        if (!PageLRU(page) && !PageCgroupUsed(pc) && memcg != root_mem_cgroup)
                pc->mem_cgroup = memcg = root_mem_cgroup;

        mz = page_cgroup_zoneinfo(memcg, page);
        lruvec = &mz->lruvec;
out:
        /*
         * Since a node can be onlined after the mem_cgroup was created,
         * we have to be prepared to initialize lruvec->zone here;
         * and if offlined then reonlined, we need to reinitialize it.
         */
        if (unlikely(lruvec->zone != zone))
                lruvec->zone = zone;
        return lruvec;
}

/**
 * mem_cgroup_update_lru_size - account for adding or removing an lru page
 * @lruvec: mem_cgroup per zone lru vector
 * @lru: index of lru list the page is sitting on
 * @nr_pages: positive when adding or negative when removing
 *
 * This function must be called when a page is added to or removed from an
 * lru list.
 */
void mem_cgroup_update_lru_size(struct lruvec *lruvec, enum lru_list lru,
                                int nr_pages)
{
        struct mem_cgroup_per_zone *mz;
        unsigned long *lru_size;

        if (mem_cgroup_disabled())
                return;

        mz = container_of(lruvec, struct mem_cgroup_per_zone, lruvec);
        lru_size = mz->lru_size + lru;
        *lru_size += nr_pages;
        VM_BUG_ON((long)(*lru_size) < 0);
}

/*
 * Checks whether given mem is same or in the root_mem_cgroup's
 * hierarchy subtree
 */
bool __mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg,
                                  struct mem_cgroup *memcg)
{
        if (root_memcg == memcg)
                return true;
        if (!root_memcg->use_hierarchy || !memcg)
                return false;
        return css_is_ancestor(&memcg->css, &root_memcg->css);
}

static bool mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg,
                                       struct mem_cgroup *memcg)
{
        bool ret;

        rcu_read_lock();
        ret = __mem_cgroup_same_or_subtree(root_memcg, memcg);
        rcu_read_unlock();
        return ret;
}

int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *memcg)
{
        int ret;
        struct mem_cgroup *curr = NULL;
        struct task_struct *p;

        p = find_lock_task_mm(task);
        if (p) {
                curr = try_get_mem_cgroup_from_mm(p->mm);
                task_unlock(p);
        } else {
                /*
                 * All threads may have already detached their mm's, but the oom
                 * killer still needs to detect if they have already been oom
                 * killed to prevent needlessly killing additional tasks.
                 */
                task_lock(task);
                curr = mem_cgroup_from_task(task);
                if (curr)
                        css_get(&curr->css);
                task_unlock(task);
        }
        if (!curr)
                return 0;
        /*
         * We should check use_hierarchy of "memcg" not "curr". Because checking
         * use_hierarchy of "curr" here make this function true if hierarchy is
         * enabled in "curr" and "curr" is a child of "memcg" in *cgroup*
         * hierarchy(even if use_hierarchy is disabled in "memcg").
         */
        ret = mem_cgroup_same_or_subtree(memcg, curr);
        css_put(&curr->css);
        return ret;
}

int mem_cgroup_inactive_anon_is_low(struct lruvec *lruvec)
{
        unsigned long inactive_ratio;
        unsigned long inactive;
        unsigned long active;
        unsigned long gb;

        inactive = mem_cgroup_get_lru_size(lruvec, LRU_INACTIVE_ANON);
        active = mem_cgroup_get_lru_size(lruvec, LRU_ACTIVE_ANON);

        gb = (inactive + active) >> (30 - PAGE_SHIFT);
        if (gb)
                inactive_ratio = int_sqrt(10 * gb);
        else
                inactive_ratio = 1;

        return inactive * inactive_ratio < active;
}

int mem_cgroup_inactive_file_is_low(struct lruvec *lruvec)
{
        unsigned long active;
        unsigned long inactive;

        inactive = mem_cgroup_get_lru_size(lruvec, LRU_INACTIVE_FILE);
        active = mem_cgroup_get_lru_size(lruvec, LRU_ACTIVE_FILE);

        return (active > inactive);
}

#define mem_cgroup_from_res_counter(counter, member)    \
        container_of(counter, struct mem_cgroup, member)

/**
 * mem_cgroup_margin - calculate chargeable space of a memory cgroup
 * @memcg: the memory cgroup
 *
 * Returns the maximum amount of memory @mem can be charged with, in
 * pages.
 */
static unsigned long mem_cgroup_margin(struct mem_cgroup *memcg)
{
        unsigned long long margin;

        margin = res_counter_margin(&memcg->res);
        if (do_swap_account)
                margin = min(margin, res_counter_margin(&memcg->memsw));
        return margin >> PAGE_SHIFT;
}

int mem_cgroup_swappiness(struct mem_cgroup *memcg)
{
        struct cgroup *cgrp = memcg->css.cgroup;

        /* root ? */
        if (cgrp->parent == NULL)
                return vm_swappiness;

        return memcg->swappiness;
}

/*
 * memcg->moving_account is used for checking possibility that some thread is
 * calling move_account(). When a thread on CPU-A starts moving pages under
 * a memcg, other threads should check memcg->moving_account under
 * rcu_read_lock(), like this:
 *
 *         CPU-A                                    CPU-B
 *                                              rcu_read_lock()
 *         memcg->moving_account+1              if (memcg->mocing_account)
 *                                                   take heavy locks.
 *         synchronize_rcu()                    update something.
 *                                              rcu_read_unlock()
 *         start move here.
 */

/* for quick checking without looking up memcg */
atomic_t memcg_moving __read_mostly;

static void mem_cgroup_start_move(struct mem_cgroup *memcg)
{
        atomic_inc(&memcg_moving);
        atomic_inc(&memcg->moving_account);
        synchronize_rcu();
}

static void mem_cgroup_end_move(struct mem_cgroup *memcg)
{
        /*
         * Now, mem_cgroup_clear_mc() may call this function with NULL.
         * We check NULL in callee rather than caller.
         */
        if (memcg) {
                atomic_dec(&memcg_moving);
                atomic_dec(&memcg->moving_account);
        }
}

/*
 * 2 routines for checking "mem" is under move_account() or not.
 *
 * mem_cgroup_stolen() -  checking whether a cgroup is mc.from or not. This
 *                        is used for avoiding races in accounting.  If true,
 *                        pc->mem_cgroup may be overwritten.
 *
 * mem_cgroup_under_move() - checking a cgroup is mc.from or mc.to or
 *                        under hierarchy of moving cgroups. This is for
 *                        waiting at hith-memory prressure caused by "move".
 */

static bool mem_cgroup_stolen(struct mem_cgroup *memcg)
{
        VM_BUG_ON(!rcu_read_lock_held());
        return atomic_read(&memcg->moving_account) > 0;
}

static bool mem_cgroup_under_move(struct mem_cgroup *memcg)
{
        struct mem_cgroup *from;
        struct mem_cgroup *to;
        bool ret = false;
        /*
         * Unlike task_move routines, we access mc.to, mc.from not under
         * mutual exclusion by cgroup_mutex. Here, we take spinlock instead.
         */
        spin_lock(&mc.lock);
        from = mc.from;
        to = mc.to;
        if (!from)
                goto unlock;

        ret = mem_cgroup_same_or_subtree(memcg, from)
                || mem_cgroup_same_or_subtree(memcg, to);
unlock:
        spin_unlock(&mc.lock);
        return ret;
}

static bool mem_cgroup_wait_acct_move(struct mem_cgroup *memcg)
{
        if (mc.moving_task && current != mc.moving_task) {
                if (mem_cgroup_under_move(memcg)) {
                        DEFINE_WAIT(wait);
                        prepare_to_wait(&mc.waitq, &wait, TASK_INTERRUPTIBLE);
                        /* moving charge context might have finished. */
                        if (mc.moving_task)
                                schedule();
                        finish_wait(&mc.waitq, &wait);
                        return true;
                }
        }
        return false;
}

/*
 * Take this lock when
 * - a code tries to modify page's memcg while it's USED.
 * - a code tries to modify page state accounting in a memcg.
 * see mem_cgroup_stolen(), too.
 */
static void move_lock_mem_cgroup(struct mem_cgroup *memcg,
                                  unsigned long *flags)
{
        spin_lock_irqsave(&memcg->move_lock, *flags);
}

static void move_unlock_mem_cgroup(struct mem_cgroup *memcg,
                                unsigned long *flags)
{
        spin_unlock_irqrestore(&memcg->move_lock, *flags);
}

/**
 * mem_cgroup_print_oom_info: Called from OOM with tasklist_lock held in read mode.
 * @memcg: The memory cgroup that went over limit
 * @p: Task that is going to be killed
 *
 * NOTE: @memcg and @p's mem_cgroup can be different when hierarchy is
 * enabled
 */
void mem_cgroup_print_oom_info(struct mem_cgroup *memcg, struct task_struct *p)
{
        struct cgroup *task_cgrp;
        struct cgroup *mem_cgrp;
        /*
         * Need a buffer in BSS, can't rely on allocations. The code relies
         * on the assumption that OOM is serialized for memory controller.
         * If this assumption is broken, revisit this code.
         */
        static char memcg_name[PATH_MAX];
        int ret;

        if (!memcg || !p)
                return;

        rcu_read_lock();

        mem_cgrp = memcg->css.cgroup;
        task_cgrp = task_cgroup(p, mem_cgroup_subsys_id);

        ret = cgroup_path(task_cgrp, memcg_name, PATH_MAX);
        if (ret < 0) {
                /*
                 * Unfortunately, we are unable to convert to a useful name
                 * But we'll still print out the usage information
                 */
                rcu_read_unlock();
                goto done;
        }
        rcu_read_unlock();

        printk(KERN_INFO "Task in %s killed", memcg_name);

        rcu_read_lock();
        ret = cgroup_path(mem_cgrp, memcg_name, PATH_MAX);
        if (ret < 0) {
                rcu_read_unlock();
                goto done;
        }
        rcu_read_unlock();

        /*
         * Continues from above, so we don't need an KERN_ level
         */
        printk(KERN_CONT " as a result of limit of %s\n", memcg_name);
done:

        printk(KERN_INFO "memory: usage %llukB, limit %llukB, failcnt %llu\n",
                res_counter_read_u64(&memcg->res, RES_USAGE) >> 10,
                res_counter_read_u64(&memcg->res, RES_LIMIT) >> 10,
                res_counter_read_u64(&memcg->res, RES_FAILCNT));
        printk(KERN_INFO "memory+swap: usage %llukB, limit %llukB, "
                "failcnt %llu\n",
                res_counter_read_u64(&memcg->memsw, RES_USAGE) >> 10,
                res_counter_read_u64(&memcg->memsw, RES_LIMIT) >> 10,
                res_counter_read_u64(&memcg->memsw, RES_FAILCNT));
}

/*
 * This function returns the number of memcg under hierarchy tree. Returns
 * 1(self count) if no children.
 */
static int mem_cgroup_count_children(struct mem_cgroup *memcg)
{
        int num = 0;
        struct mem_cgroup *iter;

        for_each_mem_cgroup_tree(iter, memcg)
                num++;
        return num;
}

/*
 * Return the memory (and swap, if configured) limit for a memcg.
 */
static u64 mem_cgroup_get_limit(struct mem_cgroup *memcg)
{
        u64 limit;

        limit = res_counter_read_u64(&memcg->res, RES_LIMIT);

        /*
         * Do not consider swap space if we cannot swap due to swappiness
         */
        if (mem_cgroup_swappiness(memcg)) {
                u64 memsw;

                limit += total_swap_pages << PAGE_SHIFT;
                memsw = res_counter_read_u64(&memcg->memsw, RES_LIMIT);

                /*
                 * If memsw is finite and limits the amount of swap space
                 * available to this memcg, return that limit.
                 */
                limit = min(limit, memsw);
        }

        return limit;
}

void mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask,
                              int order)
{
        struct mem_cgroup *iter;
        unsigned long chosen_points = 0;
        unsigned long totalpages;
        unsigned int points = 0;
        struct task_struct *chosen = NULL;

        /*
         * If current has a pending SIGKILL, then automatically select it.  The
         * goal is to allow it to allocate so that it may quickly exit and free
         * its memory.
         */
        if (fatal_signal_pending(current)) {
                set_thread_flag(TIF_MEMDIE);
                return;
        }

        check_panic_on_oom(CONSTRAINT_MEMCG, gfp_mask, order, NULL);
        totalpages = mem_cgroup_get_limit(memcg) >> PAGE_SHIFT ? : 1;
        for_each_mem_cgroup_tree(iter, memcg) {
                struct cgroup *cgroup = iter->css.cgroup;
                struct cgroup_iter it;
                struct task_struct *task;

                cgroup_iter_start(cgroup, &it);
                while ((task = cgroup_iter_next(cgroup, &it))) {
                        switch (oom_scan_process_thread(task, totalpages, NULL,
                                                        false)) {
                        case OOM_SCAN_SELECT:
                                if (chosen)
                                        put_task_struct(chosen);
                                chosen = task;
                                chosen_points = ULONG_MAX;
                                get_task_struct(chosen);
                                /* fall through */
                        case OOM_SCAN_CONTINUE:
                                continue;
                        case OOM_SCAN_ABORT:
                                cgroup_iter_end(cgroup, &it);
                                mem_cgroup_iter_break(memcg, iter);
                                if (chosen)
                                        put_task_struct(chosen);
                                return;
                        case OOM_SCAN_OK:
                                break;
                        };
                        points = oom_badness(task, memcg, NULL, totalpages);
                        if (points > chosen_points) {
                                if (chosen)
                                        put_task_struct(chosen);
                                chosen = task;
                                chosen_points = points;
                                get_task_struct(chosen);
                        }
                }
                cgroup_iter_end(cgroup, &it);
        }

        if (!chosen)
                return;
        points = chosen_points * 1000 / totalpages;
        oom_kill_process(chosen, gfp_mask, order, points, totalpages, memcg,
                         NULL, "Memory cgroup out of memory");
}

static unsigned long mem_cgroup_reclaim(struct mem_cgroup *memcg,
                                        gfp_t gfp_mask,
                                        unsigned long flags)
{
        unsigned long total = 0;
        bool noswap = false;
        int loop;

        if (flags & MEM_CGROUP_RECLAIM_NOSWAP)
                noswap = true;
        if (!(flags & MEM_CGROUP_RECLAIM_SHRINK) && memcg->memsw_is_minimum)
                noswap = true;

        for (loop = 0; loop < MEM_CGROUP_MAX_RECLAIM_LOOPS; loop++) {
                if (loop)
                        drain_all_stock_async(memcg);
                total += try_to_free_mem_cgroup_pages(memcg, gfp_mask, noswap);
                /*
                 * Allow limit shrinkers, which are triggered directly
                 * by userspace, to catch signals and stop reclaim
                 * after minimal progress, regardless of the margin.
                 */
                if (total && (flags & MEM_CGROUP_RECLAIM_SHRINK))
                        break;
                if (mem_cgroup_margin(memcg))
                        break;
                /*
                 * If nothing was reclaimed after two attempts, there
                 * may be no reclaimable pages in this hierarchy.
                 */
                if (loop && !total)
                        break;
        }
        return total;
}

/**
 * test_mem_cgroup_node_reclaimable
 * @memcg: the target memcg
 * @nid: the node ID to be checked.
 * @noswap : specify true here if the user wants flle only information.
 *
 * This function returns whether the specified memcg contains any
 * reclaimable pages on a node. Returns true if there are any reclaimable
 * pages in the node.
 */
static bool test_mem_cgroup_node_reclaimable(struct mem_cgroup *memcg,
                int nid, bool noswap)
{
        if (mem_cgroup_node_nr_lru_pages(memcg, nid, LRU_ALL_FILE))
                return true;
        if (noswap || !total_swap_pages)
                return false;
        if (mem_cgroup_node_nr_lru_pages(memcg, nid, LRU_ALL_ANON))
                return true;
        return false;

}
#if MAX_NUMNODES > 1

/*
 * Always updating the nodemask is not very good - even if we have an empty
 * list or the wrong list here, we can start from some node and traverse all
 * nodes based on the zonelist. So update the list loosely once per 10 secs.
 *
 */
static void mem_cgroup_may_update_nodemask(struct mem_cgroup *memcg)
{
        int nid;
        /*
         * numainfo_events > 0 means there was at least NUMAINFO_EVENTS_TARGET
         * pagein/pageout changes since the last update.
         */
        if (!atomic_read(&memcg->numainfo_events))
                return;
        if (atomic_inc_return(&memcg->numainfo_updating) > 1)
                return;

        /* make a nodemask where this memcg uses memory from */
        memcg->scan_nodes = node_states[N_HIGH_MEMORY];

        for_each_node_mask(nid, node_states[N_HIGH_MEMORY]) {

                if (!test_mem_cgroup_node_reclaimable(memcg, nid, false))
                        node_clear(nid, memcg->scan_nodes);
        }

        atomic_set(&memcg->numainfo_events, 0);
        atomic_set(&memcg->numainfo_updating, 0);
}

/*
 * Selecting a node where we start reclaim from. Because what we need is just
 * reducing usage counter, start from anywhere is O,K. Considering
 * memory reclaim from current node, there are pros. and cons.
 *
 * Freeing memory from current node means freeing memory from a node which
 * we'll use or we've used. So, it may make LRU bad. And if several threads
 * hit limits, it will see a contention on a node. But freeing from remote
 * node means more costs for memory reclaim because of memory latency.
 *
 * Now, we use round-robin. Better algorithm is welcomed.
 */
int mem_cgroup_select_victim_node(struct mem_cgroup *memcg)
{
        int node;

        mem_cgroup_may_update_nodemask(memcg);
        node = memcg->last_scanned_node;

        node = next_node(node, memcg->scan_nodes);
        if (node == MAX_NUMNODES)
                node = first_node(memcg->scan_nodes);
        /*
         * We call this when we hit limit, not when pages are added to LRU.
         * No LRU may hold pages because all pages are UNEVICTABLE or
         * memcg is too small and all pages are not on LRU. In that case,
         * we use curret node.
         */
        if (unlikely(node == MAX_NUMNODES))
                node = numa_node_id();

        memcg->last_scanned_node = node;
        return node;
}

/*
 * Check all nodes whether it contains reclaimable pages or not.
 * For quick scan, we make use of scan_nodes. This will allow us to skip
 * unused nodes. But scan_nodes is lazily updated and may not cotain
 * enough new information. We need to do double check.
 */
static bool mem_cgroup_reclaimable(struct mem_cgroup *memcg, bool noswap)
{
        int nid;

        /*
         * quick check...making use of scan_node.
         * We can skip unused nodes.
         */
        if (!nodes_empty(memcg->scan_nodes)) {
                for (nid = first_node(memcg->scan_nodes);
                     nid < MAX_NUMNODES;
                     nid = next_node(nid, memcg->scan_nodes)) {

                        if (test_mem_cgroup_node_reclaimable(memcg, nid, noswap))
                                return true;
                }
        }
        /*
         * Check rest of nodes.
         */
        for_each_node_state(nid, N_HIGH_MEMORY) {
                if (node_isset(nid, memcg->scan_nodes))
                        continue;
                if (test_mem_cgroup_node_reclaimable(memcg, nid, noswap))
                        return true;
        }
        return false;
}

#else
int mem_cgroup_select_victim_node(struct mem_cgroup *memcg)
{
        return 0;
}

static bool mem_cgroup_reclaimable(struct mem_cgroup *memcg, bool noswap)
{
        return test_mem_cgroup_node_reclaimable(memcg, 0, noswap);
}
#endif

static int mem_cgroup_soft_reclaim(struct mem_cgroup *root_memcg,
                                   struct zone *zone,
                                   gfp_t gfp_mask,
                                   unsigned long *total_scanned)
{
        struct mem_cgroup *victim = NULL;
        int total = 0;
        int loop = 0;
        unsigned long excess;
        unsigned long nr_scanned;
        struct mem_cgroup_reclaim_cookie reclaim = {
                .zone = zone,
                .priority = 0,
        };

        excess = res_counter_soft_limit_excess(&root_memcg->res) >> PAGE_SHIFT;

        while (1) {
                victim = mem_cgroup_iter(root_memcg, victim, &reclaim);
                if (!victim) {
                        loop++;
                        if (loop >= 2) {
                                /*
                                 * If we have not been able to reclaim
                                 * anything, it might because there are
                                 * no reclaimable pages under this hierarchy
                                 */
                                if (!total)
                                        break;
                                /*
                                 * We want to do more targeted reclaim.
                                 * excess >> 2 is not to excessive so as to
                                 * reclaim too much, nor too less that we keep
                                 * coming back to reclaim from this cgroup
                                 */
                                if (total >= (excess >> 2) ||
                                        (loop > MEM_CGROUP_MAX_RECLAIM_LOOPS))
                                        break;
                        }
                        continue;
                }
                if (!mem_cgroup_reclaimable(victim, false))
                        continue;
                total += mem_cgroup_shrink_node_zone(victim, gfp_mask, false,
                                                     zone, &nr_scanned);
                *total_scanned += nr_scanned;
                if (!res_counter_soft_limit_excess(&root_memcg->res))
                        break;
        }
        mem_cgroup_iter_break(root_memcg, victim);
        return total;
}

/*
 * Check OOM-Killer is already running under our hierarchy.
 * If someone is running, return false.
 * Has to be called with memcg_oom_lock
 */
static bool mem_cgroup_oom_lock(struct mem_cgroup *memcg)
{
        struct mem_cgroup *iter, *failed = NULL;

        for_each_mem_cgroup_tree(iter, memcg) {
                if (iter->oom_lock) {
                        /*
                         * this subtree of our hierarchy is already locked
                         * so we cannot give a lock.
                         */
                        failed = iter;
                        mem_cgroup_iter_break(memcg, iter);
                        break;
                } else
                        iter->oom_lock = true;
        }

        if (!failed)
                return true;

        /*
         * OK, we failed to lock the whole subtree so we have to clean up
         * what we set up to the failing subtree
         */
        for_each_mem_cgroup_tree(iter, memcg) {
                if (iter == failed) {
                        mem_cgroup_iter_break(memcg, iter);
                        break;
                }
                iter->oom_lock = false;
        }
        return false;
}

/*
 * Has to be called with memcg_oom_lock
 */
static int mem_cgroup_oom_unlock(struct mem_cgroup *memcg)
{
        struct mem_cgroup *iter;

        for_each_mem_cgroup_tree(iter, memcg)
                iter->oom_lock = false;
        return 0;
}

static void mem_cgroup_mark_under_oom(struct mem_cgroup *memcg)
{
        struct mem_cgroup *iter;

        for_each_mem_cgroup_tree(iter, memcg)
                atomic_inc(&iter->under_oom);
}

static void mem_cgroup_unmark_under_oom(struct mem_cgroup *memcg)
{
        struct mem_cgroup *iter;

        /*
         * When a new child is created while the hierarchy is under oom,
         * mem_cgroup_oom_lock() may not be called. We have to use
         * atomic_add_unless() here.
         */
        for_each_mem_cgroup_tree(iter, memcg)
                atomic_add_unless(&iter->under_oom, -1, 0);
}

static DEFINE_SPINLOCK(memcg_oom_lock);
static DECLARE_WAIT_QUEUE_HEAD(memcg_oom_waitq);

struct oom_wait_info {
        struct mem_cgroup *memcg;
        wait_queue_t    wait;
};

static int memcg_oom_wake_function(wait_queue_t *wait,
        unsigned mode, int sync, void *arg)
{
        struct mem_cgroup *wake_memcg = (struct mem_cgroup *)arg;
        struct mem_cgroup *oom_wait_memcg;
        struct oom_wait_info *oom_wait_info;

        oom_wait_info = container_of(wait, struct oom_wait_info, wait);
        oom_wait_memcg = oom_wait_info->memcg;

        /*
         * Both of oom_wait_info->memcg and wake_memcg are stable under us.
         * Then we can use css_is_ancestor without taking care of RCU.
         */
        if (!mem_cgroup_same_or_subtree(oom_wait_memcg, wake_memcg)
                && !mem_cgroup_same_or_subtree(wake_memcg, oom_wait_memcg))
                return 0;
        return autoremove_wake_function(wait, mode, sync, arg);
}

static void memcg_wakeup_oom(struct mem_cgroup *memcg)
{
        /* for filtering, pass "memcg" as argument. */
        __wake_up(&memcg_oom_waitq, TASK_NORMAL, 0, memcg);
}

static void memcg_oom_recover(struct mem_cgroup *memcg)
{
        if (memcg && atomic_read(&memcg->under_oom))
                memcg_wakeup_oom(memcg);
}

/*
 * try to call OOM killer. returns false if we should exit memory-reclaim loop.
 */
static bool mem_cgroup_handle_oom(struct mem_cgroup *memcg, gfp_t mask,
                                  int order)
{
        struct oom_wait_info owait;
        bool locked, need_to_kill;

        owait.memcg = memcg;
        owait.wait.flags = 0;
        owait.wait.func = memcg_oom_wake_function;
        owait.wait.private = current;
        INIT_LIST_HEAD(&owait.wait.task_list);
        need_to_kill = true;
        mem_cgroup_mark_under_oom(memcg);

        /* At first, try to OOM lock hierarchy under memcg.*/
        spin_lock(&memcg_oom_lock);
        locked = mem_cgroup_oom_lock(memcg);
        /*
         * Even if signal_pending(), we can't quit charge() loop without
         * accounting. So, UNINTERRUPTIBLE is appropriate. But SIGKILL
         * under OOM is always welcomed, use TASK_KILLABLE here.
         */
        prepare_to_wait(&memcg_oom_waitq, &owait.wait, TASK_KILLABLE);
        if (!locked || memcg->oom_kill_disable)
                need_to_kill = false;
        if (locked)
                mem_cgroup_oom_notify(memcg);
        spin_unlock(&memcg_oom_lock);

        if (need_to_kill) {
                finish_wait(&memcg_oom_waitq, &owait.wait);
                mem_cgroup_out_of_memory(memcg, mask, order);
        } else {
                schedule();
                finish_wait(&memcg_oom_waitq, &owait.wait);
        }
        spin_lock(&memcg_oom_lock);
        if (locked)
                mem_cgroup_oom_unlock(memcg);
        memcg_wakeup_oom(memcg);
        spin_unlock(&memcg_oom_lock);

        mem_cgroup_unmark_under_oom(memcg);

        if (test_thread_flag(TIF_MEMDIE) || fatal_signal_pending(current))
                return false;
        /* Give chance to dying process */
        schedule_timeout_uninterruptible(1);
        return true;
}

/*
 * Currently used to update mapped file statistics, but the routine can be
 * generalized to update other statistics as well.
 *
 * Notes: Race condition
 *
 * We usually use page_cgroup_lock() for accessing page_cgroup member but
 * it tends to be costly. But considering some conditions, we doesn't need
 * to do so _always_.
 *
 * Considering "charge", lock_page_cgroup() is not required because all
 * file-stat operations happen after a page is attached to radix-tree. There
 * are no race with "charge".
 *
 * Considering "uncharge", we know that memcg doesn't clear pc->mem_cgroup
 * at "uncharge" intentionally. So, we always see valid pc->mem_cgroup even
 * if there are race with "uncharge". Statistics itself is properly handled
 * by flags.
 *
 * Considering "move", this is an only case we see a race. To make the race
 * small, we check mm->moving_account and detect there are possibility of race
 * If there is, we take a lock.
 */

void __mem_cgroup_begin_update_page_stat(struct page *page,
                                bool *locked, unsigned long *flags)
{
        struct mem_cgroup *memcg;
        struct page_cgroup *pc;

        pc = lookup_page_cgroup(page);
again:
        memcg = pc->mem_cgroup;
        if (unlikely(!memcg || !PageCgroupUsed(pc)))
                return;
        /*
         * If this memory cgroup is not under account moving, we don't
         * need to take move_lock_mem_cgroup(). Because we already hold
         * rcu_read_lock(), any calls to move_account will be delayed until
         * rcu_read_unlock() if mem_cgroup_stolen() == true.
         */

        if (!mem_cgroup_stolen(memcg))
                return;

        move_lock_mem_cgroup(memcg, flags);
        if (memcg != pc->mem_cgroup || !PageCgroupUsed(pc)) {
                move_unlock_mem_cgroup(memcg, flags);
                goto again;
        }
        *locked = true;
}

void __mem_cgroup_end_update_page_stat(struct page *page, unsigned long *flags)
{
        struct page_cgroup *pc = lookup_page_cgroup(page);

        /*
         * It's guaranteed that pc->mem_cgroup never changes while
         * lock is held because a routine modifies pc->mem_cgroup
         * should take move_lock_mem_cgroup().
         */
        move_unlock_mem_cgroup(pc->mem_cgroup, flags);
}

void mem_cgroup_update_page_stat(struct page *page,
                                 enum mem_cgroup_page_stat_item idx, int val)
{
        struct mem_cgroup *memcg;
        struct page_cgroup *pc = lookup_page_cgroup(page);
        unsigned long uninitialized_var(flags);

        if (mem_cgroup_disabled())
                return;

        memcg = pc->mem_cgroup;
        if (unlikely(!memcg || !PageCgroupUsed(pc)))
                return;

        switch (idx) {
        case MEMCG_NR_FILE_MAPPED:
                idx = MEM_CGROUP_STAT_FILE_MAPPED;
                break;
        default:
                BUG();
        }

        this_cpu_add(memcg->stat->count[idx], val);
}

/*
 * size of first charge trial. "32" comes from vmscan.c's magic value.
 * TODO: maybe necessary to use big numbers in big irons.
 */
#define CHARGE_BATCH    32U
struct memcg_stock_pcp {
        struct mem_cgroup *cached; /* this never be root cgroup */
        unsigned int nr_pages;
        struct work_struct work;
        unsigned long flags;
#define FLUSHING_CACHED_CHARGE  0
};
static DEFINE_PER_CPU(struct memcg_stock_pcp, memcg_stock);
static DEFINE_MUTEX(percpu_charge_mutex);

/*
 * Try to consume stocked charge on this cpu. If success, one page is consumed
 * from local stock and true is returned. If the stock is 0 or charges from a
 * cgroup which is not current target, returns false. This stock will be
 * refilled.
 */
static bool consume_stock(struct mem_cgroup *memcg)
{
        struct memcg_stock_pcp *stock;
        bool ret = true;

        stock = &get_cpu_var(memcg_stock);
        if (memcg == stock->cached && stock->nr_pages)
                stock->nr_pages--;
        else /* need to call res_counter_charge */
                ret = false;
        put_cpu_var(memcg_stock);
        return ret;
}

/*
 * Returns stocks cached in percpu to res_counter and reset cached information.
 */
static void drain_stock(struct memcg_stock_pcp *stock)
{
        struct mem_cgroup *old = stock->cached;

        if (stock->nr_pages) {
                unsigned long bytes = stock->nr_pages * PAGE_SIZE;

                res_counter_uncharge(&old->res, bytes);
                if (do_swap_account)
                        res_counter_uncharge(&old->memsw, bytes);
                stock->nr_pages = 0;
        }
        stock->cached = NULL;
}

/*
 * This must be called under preempt disabled or must be called by
 * a thread which is pinned to local cpu.
 */
static void drain_local_stock(struct work_struct *dummy)
{
        struct memcg_stock_pcp *stock = &__get_cpu_var(memcg_stock);
        drain_stock(stock);
        clear_bit(FLUSHING_CACHED_CHARGE, &stock->flags);
}

/*
 * Cache charges(val) which is from res_counter, to local per_cpu area.
 * This will be consumed by consume_stock() function, later.
 */
static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
{
        struct memcg_stock_pcp *stock = &get_cpu_var(memcg_stock);

        if (stock->cached != memcg) { /* reset if necessary */
                drain_stock(stock);
                stock->cached = memcg;
        }
        stock->nr_pages += nr_pages;
        put_cpu_var(memcg_stock);
}

/*
 * Drains all per-CPU charge caches for given root_memcg resp. subtree
 * of the hierarchy under it. sync flag says whether we should block
 * until the work is done.
 */
static void drain_all_stock(struct mem_cgroup *root_memcg, bool sync)
{
        int cpu, curcpu;

        /* Notify other cpus that system-wide "drain" is running */
        get_online_cpus();
        curcpu = get_cpu();
        for_each_online_cpu(cpu) {
                struct memcg_stock_pcp *stock = &per_cpu(memcg_stock, cpu);
                struct mem_cgroup *memcg;

                memcg = stock->cached;
                if (!memcg || !stock->nr_pages)
                        continue;
                if (!mem_cgroup_same_or_subtree(root_memcg, memcg))
                        continue;
                if (!test_and_set_bit(FLUSHING_CACHED_CHARGE, &stock->flags)) {
                        if (cpu == curcpu)
                                drain_local_stock(&stock->work);
                        else
                                schedule_work_on(cpu, &stock->work);
                }
        }
        put_cpu();

        if (!sync)
                goto out;

        for_each_online_cpu(cpu) {
                struct memcg_stock_pcp *stock = &per_cpu(memcg_stock, cpu);
                if (test_bit(FLUSHING_CACHED_CHARGE, &stock->flags))
                        flush_work(&stock->work);
        }
out:
        put_online_cpus();
}

/*
 * Tries to drain stocked charges in other cpus. This function is asynchronous
 * and just put a work per cpu for draining localy on each cpu. Caller can
 * expects some charges will be back to res_counter later but cannot wait for
 * it.
 */
static void drain_all_stock_async(struct mem_cgroup *root_memcg)
{
        /*
         * If someone calls draining, avoid adding more kworker runs.
         */
        if (!mutex_trylock(&percpu_charge_mutex))
                return;
        drain_all_stock(root_memcg, false);
        mutex_unlock(&percpu_charge_mutex);
}

/* This is a synchronous drain interface. */
static void drain_all_stock_sync(struct mem_cgroup *root_memcg)
{
        /* called when force_empty is called */
        mutex_lock(&percpu_charge_mutex);
        drain_all_stock(root_memcg, true);
        mutex_unlock(&percpu_charge_mutex);
}

/*
 * This function drains percpu counter value from DEAD cpu and
 * move it to local cpu. Note that this function can be preempted.
 */
static void mem_cgroup_drain_pcp_counter(struct mem_cgroup *memcg, int cpu)
{
        int i;

        spin_lock(&memcg->pcp_counter_lock);
        for (i = 0; i < MEM_CGROUP_STAT_NSTATS; i++) {
                long x = per_cpu(memcg->stat->count[i], cpu);

                per_cpu(memcg->stat->count[i], cpu) = 0;
                memcg->nocpu_base.count[i] += x;
        }
        for (i = 0; i < MEM_CGROUP_EVENTS_NSTATS; i++) {
                unsigned long x = per_cpu(memcg->stat->events[i], cpu);

                per_cpu(memcg->stat->events[i], cpu) = 0;
                memcg->nocpu_base.events[i] += x;
        }
        spin_unlock(&memcg->pcp_counter_lock);
}

static int __cpuinit memcg_cpu_hotplug_callback(struct notifier_block *nb,
                                        unsigned long action,
                                        void *hcpu)
{
        int cpu = (unsigned long)hcpu;
        struct memcg_stock_pcp *stock;
        struct mem_cgroup *iter;

        if (action == CPU_ONLINE)
                return NOTIFY_OK;

        if (action != CPU_DEAD && action != CPU_DEAD_FROZEN)
                return NOTIFY_OK;

        for_each_mem_cgroup(iter)
                mem_cgroup_drain_pcp_counter(iter, cpu);

        stock = &per_cpu(memcg_stock, cpu);
        drain_stock(stock);
        return NOTIFY_OK;
}


/* See __mem_cgroup_try_charge() for details */
enum {
        CHARGE_OK,              /* success */
        CHARGE_RETRY,           /* need to retry but retry is not bad */
        CHARGE_NOMEM,           /* we can't do more. return -ENOMEM */
        CHARGE_WOULDBLOCK,      /* GFP_WAIT wasn't set and no enough res. */
        CHARGE_OOM_DIE,         /* the current is killed because of OOM */
};

static int mem_cgroup_do_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
                                unsigned int nr_pages, bool oom_check)
{
        unsigned long csize = nr_pages * PAGE_SIZE;
        struct mem_cgroup *mem_over_limit;
        struct res_counter *fail_res;
        unsigned long flags = 0;
        int ret;

        ret = res_counter_charge(&memcg->res, csize, &fail_res);

        if (likely(!ret)) {
                if (!do_swap_account)
                        return CHARGE_OK;
                ret = res_counter_charge(&memcg->memsw, csize, &fail_res);
                if (likely(!ret))
                        return CHARGE_OK;

                res_counter_uncharge(&memcg->res, csize);
                mem_over_limit = mem_cgroup_from_res_counter(fail_res, memsw);
                flags |= MEM_CGROUP_RECLAIM_NOSWAP;
        } else
                mem_over_limit = mem_cgroup_from_res_counter(fail_res, res);
        /*
         * nr_pages can be either a huge page (HPAGE_PMD_NR), a batch
         * of regular pages (CHARGE_BATCH), or a single regular page (1).
         *
         * Never reclaim on behalf of optional batching, retry with a
         * single page instead.
         */
        if (nr_pages == CHARGE_BATCH)
                return CHARGE_RETRY;

        if (!(gfp_mask & __GFP_WAIT))
                return CHARGE_WOULDBLOCK;

        ret = mem_cgroup_reclaim(mem_over_limit, gfp_mask, flags);
        if (mem_cgroup_margin(mem_over_limit) >= nr_pages)
                return CHARGE_RETRY;
        /*
         * Even though the limit is exceeded at this point, reclaim
         * may have been able to free some pages.  Retry the charge
         * before killing the task.
         *
         * Only for regular pages, though: huge pages are rather
         * unlikely to succeed so close to the limit, and we fall back
         * to regular pages anyway in case of failure.
         */
        if (nr_pages == 1 && ret)
                return CHARGE_RETRY;

        /*
         * At task move, charge accounts can be doubly counted. So, it's
         * better to wait until the end of task_move if something is going on.
         */
        if (mem_cgroup_wait_acct_move(mem_over_limit))
                return CHARGE_RETRY;

        /* If we don't need to call oom-killer at el, return immediately */
        if (!oom_check)
                return CHARGE_NOMEM;
        /* check OOM */
        if (!mem_cgroup_handle_oom(mem_over_limit, gfp_mask, get_order(csize)))
                return CHARGE_OOM_DIE;

        return CHARGE_RETRY;
}

/*
 * __mem_cgroup_try_charge() does
 * 1. detect memcg to be charged against from passed *mm and *ptr,
 * 2. update res_counter
 * 3. call memory reclaim if necessary.
 *
 * In some special case, if the task is fatal, fatal_signal_pending() or
 * has TIF_MEMDIE, this function returns -EINTR while writing root_mem_cgroup
 * to *ptr. There are two reasons for this. 1: fatal threads should quit as soon
 * as possible without any hazards. 2: all pages should have a valid
 * pc->mem_cgroup. If mm is NULL and the caller doesn't pass a valid memcg
 * pointer, that is treated as a charge to root_mem_cgroup.
 *
 * So __mem_cgroup_try_charge() will return
 *  0       ...  on success, filling *ptr with a valid memcg pointer.
 *  -ENOMEM ...  charge failure because of resource limits.
 *  -EINTR  ...  if thread is fatal. *ptr is filled with root_mem_cgroup.
 *
 * Unlike the exported interface, an "oom" parameter is added. if oom==true,
 * the oom-killer can be invoked.
 */
static int __mem_cgroup_try_charge(struct mm_struct *mm,
                                   gfp_t gfp_mask,
                                   unsigned int nr_pages,
                                   struct mem_cgroup **ptr,
                                   bool oom)
{
        unsigned int batch = max(CHARGE_BATCH, nr_pages);
        int nr_oom_retries = MEM_CGROUP_RECLAIM_RETRIES;
        struct mem_cgroup *memcg = NULL;
        int ret;

        /*
         * Unlike gloval-vm's OOM-kill, we're not in memory shortage
         * in system level. So, allow to go ahead dying process in addition to
         * MEMDIE process.
         */
        if (unlikely(test_thread_flag(TIF_MEMDIE)
                     || fatal_signal_pending(current)))
                goto bypass;

        /*
         * We always charge the cgroup the mm_struct belongs to.
         * The mm_struct's mem_cgroup changes on task migration if the
         * thread group leader migrates. It's possible that mm is not
         * set, if so charge the root memcg (happens for pagecache usage).
         */
        if (!*ptr && !mm)
                *ptr = root_mem_cgroup;
again:
        if (*ptr) { /* css should be a valid one */
                memcg = *ptr;
                VM_BUG_ON(css_is_removed(&memcg->css));
                if (mem_cgroup_is_root(memcg))
                        goto done;
                if (nr_pages == 1 && consume_stock(memcg))
                        goto done;
                css_get(&memcg->css);
        } else {
                struct task_struct *p;

                rcu_read_lock();
                p = rcu_dereference(mm->owner);
                /*
                 * Because we don't have task_lock(), "p" can exit.
                 * In that case, "memcg" can point to root or p can be NULL with
                 * race with swapoff. Then, we have small risk of mis-accouning.
                 * But such kind of mis-account by race always happens because
                 * we don't have cgroup_mutex(). It's overkill and we allo that
                 * small race, here.
                 * (*) swapoff at el will charge against mm-struct not against
                 * task-struct. So, mm->owner can be NULL.
                 */
                memcg = mem_cgroup_from_task(p);
                if (!memcg)
                        memcg = root_mem_cgroup;
                if (mem_cgroup_is_root(memcg)) {
                        rcu_read_unlock();
                        goto done;
                }
                if (nr_pages == 1 && consume_stock(memcg)) {
                        /*
                         * It seems dagerous to access memcg without css_get().
                         * But considering how consume_stok works, it's not
                         * necessary. If consume_stock success, some charges
                         * from this memcg are cached on this cpu. So, we
                         * don't need to call css_get()/css_tryget() before
                         * calling consume_stock().
                         */
                        rcu_read_unlock();
                        goto done;
                }
                /* after here, we may be blocked. we need to get refcnt */
                if (!css_tryget(&memcg->css)) {
                        rcu_read_unlock();
                        goto again;
                }
                rcu_read_unlock();
        }

        do {
                bool oom_check;

                /* If killed, bypass charge */
                if (fatal_signal_pending(current)) {
                        css_put(&memcg->css);
                        goto bypass;
                }

                oom_check = false;
                if (oom && !nr_oom_retries) {
                        oom_check = true;
                        nr_oom_retries = MEM_CGROUP_RECLAIM_RETRIES;
                }

                ret = mem_cgroup_do_charge(memcg, gfp_mask, batch, oom_check);
                switch (ret) {
                case CHARGE_OK:
                        break;
                case CHARGE_RETRY: /* not in OOM situation but retry */
                        batch = nr_pages;
                        css_put(&memcg->css);
                        memcg = NULL;
                        goto again;
                case CHARGE_WOULDBLOCK: /* !__GFP_WAIT */
                        css_put(&memcg->css);
                        goto nomem;
                case CHARGE_NOMEM: /* OOM routine works */
                        if (!oom) {
                                css_put(&memcg->css);
                                goto nomem;
                        }
                        /* If oom, we never return -ENOMEM */
                        nr_oom_retries--;
                        break;
                case CHARGE_OOM_DIE: /* Killed by OOM Killer */
                        css_put(&memcg->css);
                        goto bypass;
                }
        } while (ret != CHARGE_OK);

        if (batch > nr_pages)
                refill_stock(memcg, batch - nr_pages);
        css_put(&memcg->css);
done:
        *ptr = memcg;
        return 0;
nomem:
        *ptr = NULL;
        return -ENOMEM;
bypass:
        *ptr = root_mem_cgroup;
        return -EINTR;
}

/*
 * Somemtimes we have to undo a charge we got by try_charge().
 * This function is for that and do uncharge, put css's refcnt.
 * gotten by try_charge().
 */
static void __mem_cgroup_cancel_charge(struct mem_cgroup *memcg,
                                       unsigned int nr_pages)
{
        if (!mem_cgroup_is_root(memcg)) {
                unsigned long bytes = nr_pages * PAGE_SIZE;

                res_counter_uncharge(&memcg->res, bytes);
                if (do_swap_account)
                        res_counter_uncharge(&memcg->memsw, bytes);
        }
}

/*
 * Cancel chrages in this cgroup....doesn't propagate to parent cgroup.
 * This is useful when moving usage to parent cgroup.
 */
static void __mem_cgroup_cancel_local_charge(struct mem_cgroup *memcg,
                                        unsigned int nr_pages)
{
        unsigned long bytes = nr_pages * PAGE_SIZE;

        if (mem_cgroup_is_root(memcg))
                return;

        res_counter_uncharge_until(&memcg->res, memcg->res.parent, bytes);
        if (do_swap_account)
                res_counter_uncharge_until(&memcg->memsw,
                                                memcg->memsw.parent, bytes);
}

/*
 * A helper function to get mem_cgroup from ID. must be called under
 * rcu_read_lock(). The caller must check css_is_removed() or some if
 * it's concern. (dropping refcnt from swap can be called against removed
 * memcg.)
 */
static struct mem_cgroup *mem_cgroup_lookup(unsigned short id)
{
        struct cgroup_subsys_state *css;

        /* ID 0 is unused ID */
        if (!id)
                return NULL;
        css = css_lookup(&mem_cgroup_subsys, id);
        if (!css)
                return NULL;
        return mem_cgroup_from_css(css);
}

struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page)
{
        struct mem_cgroup *memcg = NULL;
        struct page_cgroup *pc;
        unsigned short id;
        swp_entry_t ent;

        VM_BUG_ON(!PageLocked(page));

        pc = lookup_page_cgroup(page);
        lock_page_cgroup(pc);
        if (PageCgroupUsed(pc)) {
                memcg = pc->mem_cgroup;
                if (memcg && !css_tryget(&memcg->css))
                        memcg = NULL;
        } else if (PageSwapCache(page)) {
                ent.val = page_private(page);
                id = lookup_swap_cgroup_id(ent);
                rcu_read_lock();
                memcg = mem_cgroup_lookup(id);
                if (memcg && !css_tryget(&memcg->css))
                        memcg = NULL;
                rcu_read_unlock();
        }
        unlock_page_cgroup(pc);
        return memcg;
}

static void __mem_cgroup_commit_charge(struct mem_cgroup *memcg,
                                       struct page *page,
                                       unsigned int nr_pages,
                                       enum charge_type ctype,
                                       bool lrucare)
{
        struct page_cgroup *pc = lookup_page_cgroup(page);
        struct zone *uninitialized_var(zone);
        struct lruvec *lruvec;
        bool was_on_lru = false;
        bool anon;

        lock_page_cgroup(pc);
        VM_BUG_ON(PageCgroupUsed(pc));
        /*
         * we don't need page_cgroup_lock about tail pages, becase they are not
         * accessed by any other context at this point.
         */

        /*
         * In some cases, SwapCache and FUSE(splice_buf->radixtree), the page
         * may already be on some other mem_cgroup's LRU.  Take care of it.
         */
        if (lrucare) {
                zone = page_zone(page);
                spin_lock_irq(&zone->lru_lock);
                if (PageLRU(page)) {
                        lruvec = mem_cgroup_zone_lruvec(zone, pc->mem_cgroup);
                        ClearPageLRU(page);
                        del_page_from_lru_list(page, lruvec, page_lru(page));
                        was_on_lru = true;
                }
        }

        pc->mem_cgroup = memcg;
        /*
         * We access a page_cgroup asynchronously without lock_page_cgroup().
         * Especially when a page_cgroup is taken from a page, pc->mem_cgroup
         * is accessed after testing USED bit. To make pc->mem_cgroup visible
         * before USED bit, we need memory barrier here.
         * See mem_cgroup_add_lru_list(), etc.
         */
        smp_wmb();
        SetPageCgroupUsed(pc);

        if (lrucare) {
                if (was_on_lru) {
                        lruvec = mem_cgroup_zone_lruvec(zone, pc->mem_cgroup);
                        VM_BUG_ON(PageLRU(page));
                        SetPageLRU(page);
                        add_page_to_lru_list(page, lruvec, page_lru(page));
                }
                spin_unlock_irq(&zone->lru_lock);
        }

        if (ctype == MEM_CGROUP_CHARGE_TYPE_ANON)
                anon = true;
        else
                anon = false;

        mem_cgroup_charge_statistics(memcg, anon, nr_pages);
        unlock_page_cgroup(pc);

        /*
         * "charge_statistics" updated event counter. Then, check it.
         * Insert ancestor (and ancestor's ancestors), to softlimit RB-tree.
         * if they exceeds softlimit.
         */
        memcg_check_events(memcg, page);
}

#ifdef CONFIG_TRANSPARENT_HUGEPAGE

#define PCGF_NOCOPY_AT_SPLIT (1 << PCG_LOCK | 1 << PCG_MIGRATION)
/*
 * Because tail pages are not marked as "used", set it. We're under
 * zone->lru_lock, 'splitting on pmd' and compound_lock.
 * charge/uncharge will be never happen and move_account() is done under
 * compound_lock(), so we don't have to take care of races.
 */
void mem_cgroup_split_huge_fixup(struct page *head)
{
        struct page_cgroup *head_pc = lookup_page_cgroup(head);
        struct page_cgroup *pc;
        int i;

        if (mem_cgroup_disabled())
                return;
        for (i = 1; i < HPAGE_PMD_NR; i++) {
                pc = head_pc + i;
                pc->mem_cgroup = head_pc->mem_cgroup;
                smp_wmb();/* see __commit_charge() */
                pc->flags = head_pc->flags & ~PCGF_NOCOPY_AT_SPLIT;
        }
}
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */

/**
 * mem_cgroup_move_account - move account of the page
 * @page: the page
 * @nr_pages: number of regular pages (>1 for huge pages)
 * @pc: page_cgroup of the page.
 * @from: mem_cgroup which the page is moved from.
 * @to: mem_cgroup which the page is moved to. @from != @to.
 *
 * The caller must confirm following.
 * - page is not on LRU (isolate_page() is useful.)
 * - compound_lock is held when nr_pages > 1
 *
 * This function doesn't do "charge" to new cgroup and doesn't do "uncharge"
 * from old cgroup.
 */
static int mem_cgroup_move_account(struct page *page,
                                   unsigned int nr_pages,
                                   struct page_cgroup *pc,
                                   struct mem_cgroup *from,
                                   struct mem_cgroup *to)
{
        unsigned long flags;
        int ret;
        bool anon = PageAnon(page);

        VM_BUG_ON(from == to);
        VM_BUG_ON(PageLRU(page));
        /*
         * The page is isolated from LRU. So, collapse function
         * will not handle this page. But page splitting can happen.
         * Do this check under compound_page_lock(). The caller should
         * hold it.
         */
        ret = -EBUSY;
        if (nr_pages > 1 && !PageTransHuge(page))
                goto out;

        lock_page_cgroup(pc);

        ret = -EINVAL;
        if (!PageCgroupUsed(pc) || pc->mem_cgroup != from)
                goto unlock;

        move_lock_mem_cgroup(from, &flags);

        if (!anon && page_mapped(page)) {
                /* Update mapped_file data for mem_cgroup */
                preempt_disable();
                __this_cpu_dec(from->stat->count[MEM_CGROUP_STAT_FILE_MAPPED]);
                __this_cpu_inc(to->stat->count[MEM_CGROUP_STAT_FILE_MAPPED]);
                preempt_enable();
        }
        mem_cgroup_charge_statistics(from, anon, -nr_pages);

        /* caller should have done css_get */
        pc->mem_cgroup = to;
        mem_cgroup_charge_statistics(to, anon, nr_pages);
        /*
         * We charges against "to" which may not have any tasks. Then, "to"
         * can be under rmdir(). But in current implementation, caller of
         * this function is just force_empty() and move charge, so it's
         * guaranteed that "to" is never removed. So, we don't check rmdir
         * status here.
         */
        move_unlock_mem_cgroup(from, &flags);
        ret = 0;
unlock:
        unlock_page_cgroup(pc);
        /*
         * check events
         */
        memcg_check_events(to, page);
        memcg_check_events(from, page);
out:
        return ret;
}

/*
 * move charges to its parent.
 */

static int mem_cgroup_move_parent(struct page *page,
                                  struct page_cgroup *pc,
                                  struct mem_cgroup *child)
{
        struct mem_cgroup *parent;
        unsigned int nr_pages;
        unsigned long uninitialized_var(flags);
        int ret;

        /* Is ROOT ? */
        if (mem_cgroup_is_root(child))
                return -EINVAL;

        ret = -EBUSY;
        if (!get_page_unless_zero(page))
                goto out;
        if (isolate_lru_page(page))
                goto put;

        nr_pages = hpage_nr_pages(page);

        parent = parent_mem_cgroup(child);
        /*
         * If no parent, move charges to root cgroup.
         */
        if (!parent)
                parent = root_mem_cgroup;

        if (nr_pages > 1)
                flags = compound_lock_irqsave(page);

        ret = mem_cgroup_move_account(page, nr_pages,
                                pc, child, parent);
        if (!ret)
                __mem_cgroup_cancel_local_charge(child, nr_pages);

        if (nr_pages > 1)
                compound_unlock_irqrestore(page, flags);
        putback_lru_page(page);
put:
        put_page(page);
out:
        return ret;
}

/*
 * Charge the memory controller for page usage.
 * Return
 * 0 if the charge was successful
 * < 0 if the cgroup is over its limit
 */
static int mem_cgroup_charge_common(struct page *page, struct mm_struct *mm,
                                gfp_t gfp_mask, enum charge_type ctype)
{
        struct mem_cgroup *memcg = NULL;
        unsigned int nr_pages = 1;
        bool oom = true;
        int ret;

        if (PageTransHuge(page)) {
                nr_pages <<= compound_order(page);
                VM_BUG_ON(!PageTransHuge(page));
                /*
                 * Never OOM-kill a process for a huge page.  The
                 * fault handler will fall back to regular pages.
                 */
                oom = false;
        }

        ret = __mem_cgroup_try_charge(mm, gfp_mask, nr_pages, &memcg, oom);
        if (ret == -ENOMEM)
                return ret;
        __mem_cgroup_commit_charge(memcg, page, nr_pages, ctype, false);
        return 0;
}

int mem_cgroup_newpage_charge(struct page *page,
                              struct mm_struct *mm, gfp_t gfp_mask)
{
        if (mem_cgroup_disabled())
                return 0;
        VM_BUG_ON(page_mapped(page));
        VM_BUG_ON(page->mapping && !PageAnon(page));
        VM_BUG_ON(!mm);
        return mem_cgroup_charge_common(page, mm, gfp_mask,
                                        MEM_CGROUP_CHARGE_TYPE_ANON);
}

/*
 * While swap-in, try_charge -> commit or cancel, the page is locked.
 * And when try_charge() successfully returns, one refcnt to memcg without
 * struct page_cgroup is acquired. This refcnt will be consumed by
 * "commit()" or removed by "cancel()"
 */
static int __mem_cgroup_try_charge_swapin(struct mm_struct *mm,
                                          struct page *page,
                                          gfp_t mask,
                                          struct mem_cgroup **memcgp)
{
        struct mem_cgroup *memcg;
        struct page_cgroup *pc;
        int ret;

        pc = lookup_page_cgroup(page);
        /*
         * Every swap fault against a single page tries to charge the
         * page, bail as early as possible.  shmem_unuse() encounters
         * already charged pages, too.  The USED bit is protected by
         * the page lock, which serializes swap cache removal, which
         * in turn serializes uncharging.
         */
        if (PageCgroupUsed(pc))
                return 0;
        if (!do_swap_account)
                goto charge_cur_mm;
        memcg = try_get_mem_cgroup_from_page(page);
        if (!memcg)
                goto charge_cur_mm;
        *memcgp = memcg;
        ret = __mem_cgroup_try_charge(NULL, mask, 1, memcgp, true);
        css_put(&memcg->css);
        if (ret == -EINTR)
                ret = 0;
        return ret;
charge_cur_mm:
        ret = __mem_cgroup_try_charge(mm, mask, 1, memcgp, true);
        if (ret == -EINTR)
                ret = 0;
        return ret;
}

int mem_cgroup_try_charge_swapin(struct mm_struct *mm, struct page *page,
                                 gfp_t gfp_mask, struct mem_cgroup **memcgp)
{
        *memcgp = NULL;
        if (mem_cgroup_disabled())
                return 0;
        /*
         * A racing thread's fault, or swapoff, may have already
         * updated the pte, and even removed page from swap cache: in
         * those cases unuse_pte()'s pte_same() test will fail; but
         * there's also a KSM case which does need to charge the page.
         */
        if (!PageSwapCache(page)) {
                int ret;

                ret = __mem_cgroup_try_charge(mm, gfp_mask, 1, memcgp, true);
                if (ret == -EINTR)
                        ret = 0;
                return ret;
        }
        return __mem_cgroup_try_charge_swapin(mm, page, gfp_mask, memcgp);
}

void mem_cgroup_cancel_charge_swapin(struct mem_cgroup *memcg)
{
        if (mem_cgroup_disabled())
                return;
        if (!memcg)
                return;
        __mem_cgroup_cancel_charge(memcg, 1);
}

static void
__mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *memcg,
                                        enum charge_type ctype)
{
        if (mem_cgroup_disabled())
                return;
        if (!memcg)
                return;
        cgroup_exclude_rmdir(&memcg->css);

        __mem_cgroup_commit_charge(memcg, page, 1, ctype, true);
        /*
         * Now swap is on-memory. This means this page may be
         * counted both as mem and swap....double count.
         * Fix it by uncharging from memsw. Basically, this SwapCache is stable
         * under lock_page(). But in do_swap_page()::memory.c, reuse_swap_page()
         * may call delete_from_swap_cache() before reach here.
         */
        if (do_swap_account && PageSwapCache(page)) {
                swp_entry_t ent = {.val = page_private(page)};
                mem_cgroup_uncharge_swap(ent);
        }
        /*
         * At swapin, we may charge account against cgroup which has no tasks.
         * So, rmdir()->pre_destroy() can be called while we do this charge.
         * In that case, we need to call pre_destroy() again. check it here.
         */
        cgroup_release_and_wakeup_rmdir(&memcg->css);
}

void mem_cgroup_commit_charge_swapin(struct page *page,
                                     struct mem_cgroup *memcg)
{
        __mem_cgroup_commit_charge_swapin(page, memcg,
                                          MEM_CGROUP_CHARGE_TYPE_ANON);
}

int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
                                gfp_t gfp_mask)
{
        struct mem_cgroup *memcg = NULL;
        enum charge_type type = MEM_CGROUP_CHARGE_TYPE_CACHE;
        int ret;

        if (mem_cgroup_disabled())
                return 0;
        if (PageCompound(page))
                return 0;

        if (!PageSwapCache(page))
                ret = mem_cgroup_charge_common(page, mm, gfp_mask, type);
        else { /* page is swapcache/shmem */
                ret = __mem_cgroup_try_charge_swapin(mm, page,
                                                     gfp_mask, &memcg);
                if (!ret)
                        __mem_cgroup_commit_charge_swapin(page, memcg, type);
        }
        return ret;
}

static void mem_cgroup_do_uncharge(struct mem_cgroup *memcg,
                                   unsigned int nr_pages,
                                   const enum charge_type ctype)
{
        struct memcg_batch_info *batch = NULL;
        bool uncharge_memsw = true;

        /* If swapout, usage of swap doesn't decrease */
        if (!do_swap_account || ctype == MEM_CGROUP_CHARGE_TYPE_SWAPOUT)
                uncharge_memsw = false;

        batch = &current->memcg_batch;
        /*
         * In usual, we do css_get() when we remember memcg pointer.
         * But in this case, we keep res->usage until end of a series of
         * uncharges. Then, it's ok to ignore memcg's refcnt.
         */
        if (!batch->memcg)
                batch->memcg = memcg;
        /*
         * do_batch > 0 when unmapping pages or inode invalidate/truncate.
         * In those cases, all pages freed continuously can be expected to be in
         * the same cgroup and we have chance to coalesce uncharges.
         * But we do uncharge one by one if this is killed by OOM(TIF_MEMDIE)
         * because we want to do uncharge as soon as possible.
         */

        if (!batch->do_batch || test_thread_flag(TIF_MEMDIE))
                goto direct_uncharge;

        if (nr_pages > 1)
                goto direct_uncharge;

        /*
         * In typical case, batch->memcg == mem. This means we can
         * merge a series of uncharges to an uncharge of res_counter.
         * If not, we uncharge res_counter ony by one.
         */
        if (batch->memcg != memcg)
                goto direct_uncharge;
        /* remember freed charge and uncharge it later */
        batch->nr_pages++;

        if (uncharge_memsw)
                batch->memsw_nr_pages++;
        return;
direct_uncharge:
        res_counter_uncharge(&memcg->res, nr_pages * PAGE_SIZE);
        if (uncharge_memsw)
                res_counter_uncharge(&memcg->memsw, nr_pages * PAGE_SIZE);
        if (unlikely(batch->memcg != memcg))
                memcg_oom_recover(memcg);
}

/*
 * uncharge if !page_mapped(page)
 */
static struct mem_cgroup *
__mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype,
                             bool end_migration)
{
        struct mem_cgroup *memcg = NULL;
        unsigned int nr_pages = 1;
        struct page_cgroup *pc;
        bool anon;

        if (mem_cgroup_disabled())
                return NULL;

        VM_BUG_ON(PageSwapCache(page));

        if (PageTransHuge(page)) {
                nr_pages <<= compound_order(page);
                VM_BUG_ON(!PageTransHuge(page));
        }
        /*
         * Check if our page_cgroup is valid
         */
        pc = lookup_page_cgroup(page);
        if (unlikely(!PageCgroupUsed(pc)))
                return NULL;

        lock_page_cgroup(pc);

        memcg = pc->mem_cgroup;

        if (!PageCgroupUsed(pc))
                goto unlock_out;

        anon = PageAnon(page);

        switch (ctype) {
        case MEM_CGROUP_CHARGE_TYPE_ANON:
                /*
                 * Generally PageAnon tells if it's the anon statistics to be
                 * updated; but sometimes e.g. mem_cgroup_uncharge_page() is
                 * used before page reached the stage of being marked PageAnon.
                 */
                anon = true;
                /* fallthrough */
        case MEM_CGROUP_CHARGE_TYPE_DROP:
                /* See mem_cgroup_prepare_migration() */
                if (page_mapped(page))
                        goto unlock_out;
                /*
                 * Pages under migration may not be uncharged.  But
                 * end_migration() /must/ be the one uncharging the
                 * unused post-migration page and so it has to call
                 * here with the migration bit still set.  See the
                 * res_counter handling below.
                 */
                if (!end_migration && PageCgroupMigration(pc))
                        goto unlock_out;
                break;
        case MEM_CGROUP_CHARGE_TYPE_SWAPOUT:
                if (!PageAnon(page)) {  /* Shared memory */
                        if (page->mapping && !page_is_file_cache(page))
                                goto unlock_out;
                } else if (page_mapped(page)) /* Anon */
                                goto unlock_out;
                break;
        default:
                break;
        }

        mem_cgroup_charge_statistics(memcg, anon, -nr_pages);

        ClearPageCgroupUsed(pc);
        /*
         * pc->mem_cgroup is not cleared here. It will be accessed when it's
         * freed from LRU. This is safe because uncharged page is expected not
         * to be reused (freed soon). Exception is SwapCache, it's handled by
         * special functions.
         */

        unlock_page_cgroup(pc);
        /*
         * even after unlock, we have memcg->res.usage here and this memcg
         * will never be freed.
         */
        memcg_check_events(memcg, page);
        if (do_swap_account && ctype == MEM_CGROUP_CHARGE_TYPE_SWAPOUT) {
                mem_cgroup_swap_statistics(memcg, true);
                mem_cgroup_get(memcg);
        }
        /*
         * Migration does not charge the res_counter for the
         * replacement page, so leave it alone when phasing out the
         * page that is unused after the migration.
         */
        if (!end_migration && !mem_cgroup_is_root(memcg))
                mem_cgroup_do_uncharge(memcg, nr_pages, ctype);

        return memcg;

unlock_out:
        unlock_page_cgroup(pc);
        return NULL;
}

void mem_cgroup_uncharge_page(struct page *page)
{
        /* early check. */
        if (page_mapped(page))
                return;
        VM_BUG_ON(page->mapping && !PageAnon(page));
        if (PageSwapCache(page))
                return;
        __mem_cgroup_uncharge_common(page, MEM_CGROUP_CHARGE_TYPE_ANON, false);
}

void mem_cgroup_uncharge_cache_page(struct page *page)
{
        VM_BUG_ON(page_mapped(page));
        VM_BUG_ON(page->mapping);
        __mem_cgroup_uncharge_common(page, MEM_CGROUP_CHARGE_TYPE_CACHE, false);
}

/*
 * Batch_start/batch_end is called in unmap_page_range/invlidate/trucate.
 * In that cases, pages are freed continuously and we can expect pages
 * are in the same memcg. All these calls itself limits the number of
 * pages freed at once, then uncharge_start/end() is called properly.
 * This may be called prural(2) times in a context,
 */

void mem_cgroup_uncharge_start(void)
{
        current->memcg_batch.do_batch++;
        /* We can do nest. */
        if (current->memcg_batch.do_batch == 1) {
                current->memcg_batch.memcg = NULL;
                current->memcg_batch.nr_pages = 0;
                current->memcg_batch.memsw_nr_pages = 0;
        }
}

void mem_cgroup_uncharge_end(void)
{
        struct memcg_batch_info *batch = &current->memcg_batch;

        if (!batch->do_batch)
                return;

        batch->do_batch--;
        if (batch->do_batch) /* If stacked, do nothing. */
                return;

        if (!batch->memcg)
                return;
        /*
         * This "batch->memcg" is valid without any css_get/put etc...
         * bacause we hide charges behind us.
         */
        if (batch->nr_pages)
                res_counter_uncharge(&batch->memcg->res,
                                     batch->nr_pages * PAGE_SIZE);
        if (batch->memsw_nr_pages)
                res_counter_uncharge(&batch->memcg->memsw,
                                     batch->memsw_nr_pages * PAGE_SIZE);
        memcg_oom_recover(batch->memcg);
        /* forget this pointer (for sanity check) */
        batch->memcg = NULL;
}

#ifdef CONFIG_SWAP
/*
 * called after __delete_from_swap_cache() and drop "page" account.
 * memcg information is recorded to swap_cgroup of "ent"
 */
void
mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent, bool swapout)
{
        struct mem_cgroup *memcg;
        int ctype = MEM_CGROUP_CHARGE_TYPE_SWAPOUT;

        if (!swapout) /* this was a swap cache but the swap is unused ! */
                ctype = MEM_CGROUP_CHARGE_TYPE_DROP;

        memcg = __mem_cgroup_uncharge_common(page, ctype, false);

        /*
         * record memcg information,  if swapout && memcg != NULL,
         * mem_cgroup_get() was called in uncharge().
         */
        if (do_swap_account && swapout && memcg)
                swap_cgroup_record(ent, css_id(&memcg->css));
}
#endif

#ifdef CONFIG_MEMCG_SWAP
/*
 * called from swap_entry_free(). remove record in swap_cgroup and
 * uncharge "memsw" account.
 */
void mem_cgroup_uncharge_swap(swp_entry_t ent)
{
        struct mem_cgroup *memcg;
        unsigned short id;

        if (!do_swap_account)
                return;

        id = swap_cgroup_record(ent, 0);
        rcu_read_lock();
        memcg = mem_cgroup_lookup(id);
        if (memcg) {
                /*
                 * We uncharge this because swap is freed.
                 * This memcg can be obsolete one. We avoid calling css_tryget
                 */
                if (!mem_cgroup_is_root(memcg))
                        res_counter_uncharge(&memcg->memsw, PAGE_SIZE);
                mem_cgroup_swap_statistics(memcg, false);
                mem_cgroup_put(memcg);
        }
        rcu_read_unlock();
}

/**
 * mem_cgroup_move_swap_account - move swap charge and swap_cgroup's record.
 * @entry: swap entry to be moved
 * @from:  mem_cgroup which the entry is moved from
 * @to:  mem_cgroup which the entry is moved to
 *
 * It succeeds only when the swap_cgroup's record for this entry is the same
 * as the mem_cgroup's id of @from.
 *
 * Returns 0 on success, -EINVAL on failure.
 *
 * The caller must have charged to @to, IOW, called res_counter_charge() about
 * both res and memsw, and called css_get().
 */
static int mem_cgroup_move_swap_account(swp_entry_t entry,
                                struct mem_cgroup *from, struct mem_cgroup *to)
{
        unsigned short old_id, new_id;

        old_id = css_id(&from->css);
        new_id = css_id(&to->css);

        if (swap_cgroup_cmpxchg(entry, old_id, new_id) == old_id) {
                mem_cgroup_swap_statistics(from, false);
                mem_cgroup_swap_statistics(to, true);
                /*
                 * This function is only called from task migration context now.
                 * It postpones res_counter and refcount handling till the end
                 * of task migration(mem_cgroup_clear_mc()) for performance
                 * improvement. But we cannot postpone mem_cgroup_get(to)
                 * because if the process that has been moved to @to does
                 * swap-in, the refcount of @to might be decreased to 0.
                 */
                mem_cgroup_get(to);
                return 0;
        }
        return -EINVAL;
}
#else
static inline int mem_cgroup_move_swap_account(swp_entry_t entry,
                                struct mem_cgroup *from, struct mem_cgroup *to)
{
        return -EINVAL;
}
#endif

/*
 * Before starting migration, account PAGE_SIZE to mem_cgroup that the old
 * page belongs to.
 */
void mem_cgroup_prepare_migration(struct page *page, struct page *newpage,
                                  struct mem_cgroup **memcgp)
{
        struct mem_cgroup *memcg = NULL;
        struct page_cgroup *pc;
        enum charge_type ctype;

        *memcgp = NULL;

        VM_BUG_ON(PageTransHuge(page));
        if (mem_cgroup_disabled())
                return;

        pc = lookup_page_cgroup(page);
        lock_page_cgroup(pc);
        if (PageCgroupUsed(pc)) {
                memcg = pc->mem_cgroup;
                css_get(&memcg->css);
                /*
                 * At migrating an anonymous page, its mapcount goes down
                 * to 0 and uncharge() will be called. But, even if it's fully
                 * unmapped, migration may fail and this page has to be
                 * charged again. We set MIGRATION flag here and delay uncharge
                 * until end_migration() is called
                 *
                 * Corner Case Thinking
                 * A)
                 * When the old page was mapped as Anon and it's unmap-and-freed
                 * while migration was ongoing.
                 * If unmap finds the old page, uncharge() of it will be delayed
                 * until end_migration(). If unmap finds a new page, it's
                 * uncharged when it make mapcount to be 1->0. If unmap code
                 * finds swap_migration_entry, the new page will not be mapped
                 * and end_migration() will find it(mapcount==0).
                 *
                 * B)
                 * When the old page was mapped but migraion fails, the kernel
                 * remaps it. A charge for it is kept by MIGRATION flag even
                 * if mapcount goes down to 0. We can do remap successfully
                 * without charging it again.
                 *
                 * C)
                 * The "old" page is under lock_page() until the end of
                 * migration, so, the old page itself will not be swapped-out.
                 * If the new page is swapped out before end_migraton, our
                 * hook to usual swap-out path will catch the event.
                 */
                if (PageAnon(page))
                        SetPageCgroupMigration(pc);
        }
        unlock_page_cgroup(pc);
        /*
         * If the page is not charged at this point,
         * we return here.
         */
        if (!memcg)
                return;

        *memcgp = memcg;
        /*
         * We charge new page before it's used/mapped. So, even if unlock_page()
         * is called before end_migration, we can catch all events on this new
         * page. In the case new page is migrated but not remapped, new page's
         * mapcount will be finally 0 and we call uncharge in end_migration().
         */
        if (PageAnon(page))
                ctype = MEM_CGROUP_CHARGE_TYPE_ANON;
        else
                ctype = MEM_CGROUP_CHARGE_TYPE_CACHE;
        /*
         * The page is committed to the memcg, but it's not actually
         * charged to the res_counter since we plan on replacing the
         * old one and only one page is going to be left afterwards.
         */
        __mem_cgroup_commit_charge(memcg, newpage, 1, ctype, false);
}

/* remove redundant charge if migration failed*/
void mem_cgroup_end_migration(struct mem_cgroup *memcg,
        struct page *oldpage, struct page *newpage, bool migration_ok)
{
        struct page *used, *unused;
        struct page_cgroup *pc;
        bool anon;

        if (!memcg)
                return;
        /* blocks rmdir() */
        cgroup_exclude_rmdir(&memcg->css);
        if (!migration_ok) {
                used = oldpage;
                unused = newpage;
        } else {
                used = newpage;
                unused = oldpage;
        }
        anon = PageAnon(used);
        __mem_cgroup_uncharge_common(unused,
                                     anon ? MEM_CGROUP_CHARGE_TYPE_ANON
                                     : MEM_CGROUP_CHARGE_TYPE_CACHE,
                                     true);
        css_put(&memcg->css);
        /*
         * We disallowed uncharge of pages under migration because mapcount
         * of the page goes down to zero, temporarly.
         * Clear the flag and check the page should be charged.
         */
        pc = lookup_page_cgroup(oldpage);
        lock_page_cgroup(pc);
        ClearPageCgroupMigration(pc);
        unlock_page_cgroup(pc);

        /*
         * If a page is a file cache, radix-tree replacement is very atomic
         * and we can skip this check. When it was an Anon page, its mapcount
         * goes down to 0. But because we added MIGRATION flage, it's not
         * uncharged yet. There are several case but page->mapcount check
         * and USED bit check in mem_cgroup_uncharge_page() will do enough
         * check. (see prepare_charge() also)
         */
        if (anon)
                mem_cgroup_uncharge_page(used);
        /*
         * At migration, we may charge account against cgroup which has no
         * tasks.
         * So, rmdir()->pre_destroy() can be called while we do this charge.
         * In that case, we need to call pre_destroy() again. check it here.
         */
        cgroup_release_and_wakeup_rmdir(&memcg->css);
}

/*
 * At replace page cache, newpage is not under any memcg but it's on
 * LRU. So, this function doesn't touch res_counter but handles LRU
 * in correct way. Both pages are locked so we cannot race with uncharge.
 */
void mem_cgroup_replace_page_cache(struct page *oldpage,
                                  struct page *newpage)
{
        struct mem_cgroup *memcg = NULL;
        struct page_cgroup *pc;
        enum charge_type type = MEM_CGROUP_CHARGE_TYPE_CACHE;

        if (mem_cgroup_disabled())
                return;

        pc = lookup_page_cgroup(oldpage);
        /* fix accounting on old pages */
        lock_page_cgroup(pc);
        if (PageCgroupUsed(pc)) {
                memcg = pc->mem_cgroup;
                mem_cgroup_charge_statistics(memcg, false, -1);
                ClearPageCgroupUsed(pc);
        }
        unlock_page_cgroup(pc);

        /*
         * When called from shmem_replace_page(), in some cases the
         * oldpage has already been charged, and in some cases not.
         */
        if (!memcg)
                return;
        /*
         * Even if newpage->mapping was NULL before starting replacement,
         * the newpage may be on LRU(or pagevec for LRU) already. We lock
         * LRU while we overwrite pc->mem_cgroup.
         */
        __mem_cgroup_commit_charge(memcg, newpage, 1, type, true);
}

#ifdef CONFIG_DEBUG_VM
static struct page_cgroup *lookup_page_cgroup_used(struct page *page)
{
        struct page_cgroup *pc;

        pc = lookup_page_cgroup(page);
        /*
         * Can be NULL while feeding pages into the page allocator for
         * the first time, i.e. during boot or memory hotplug;
         * or when mem_cgroup_disabled().
         */
        if (likely(pc) && PageCgroupUsed(pc))
                return pc;
        return NULL;
}

bool mem_cgroup_bad_page_check(struct page *page)
{
        if (mem_cgroup_disabled())
                return false;

        return lookup_page_cgroup_used(page) != NULL;
}

void mem_cgroup_print_bad_page(struct page *page)
{
        struct page_cgroup *pc;

        pc = lookup_page_cgroup_used(page);
        if (pc) {
                printk(KERN_ALERT "pc:%p pc->flags:%lx pc->mem_cgroup:%p\n",
                       pc, pc->flags, pc->mem_cgroup);
        }
}
#endif

static DEFINE_MUTEX(set_limit_mutex);

static int mem_cgroup_resize_limit(struct mem_cgroup *memcg,
                                unsigned long long val)
{
        int retry_count;
        u64 memswlimit, memlimit;
        int ret = 0;
        int children = mem_cgroup_count_children(memcg);
        u64 curusage, oldusage;
        int enlarge;

        /*
         * For keeping hierarchical_reclaim simple, how long we should retry
         * is depends on callers. We set our retry-count to be function
         * of # of children which we should visit in this loop.
         */
        retry_count = MEM_CGROUP_RECLAIM_RETRIES * children;

        oldusage = res_counter_read_u64(&memcg->res, RES_USAGE);

        enlarge = 0;
        while (retry_count) {
                if (signal_pending(current)) {
                        ret = -EINTR;
                        break;
                }
                /*
                 * Rather than hide all in some function, I do this in
                 * open coded manner. You see what this really does.
                 * We have to guarantee memcg->res.limit <= memcg->memsw.limit.
                 */
                mutex_lock(&set_limit_mutex);
                memswlimit = res_counter_read_u64(&memcg->memsw, RES_LIMIT);
                if (memswlimit < val) {
                        ret = -EINVAL;
                        mutex_unlock(&set_limit_mutex);
                        break;
                }

                memlimit = res_counter_read_u64(&memcg->res, RES_LIMIT);
                if (memlimit < val)
                        enlarge = 1;

                ret = res_counter_set_limit(&memcg->res, val);
                if (!ret) {
                        if (memswlimit == val)
                                memcg->memsw_is_minimum = true;
                        else
                                memcg->memsw_is_minimum = false;
                }
                mutex_unlock(&set_limit_mutex);

                if (!ret)
                        break;

                mem_cgroup_reclaim(memcg, GFP_KERNEL,
                                   MEM_CGROUP_RECLAIM_SHRINK);
                curusage = res_counter_read_u64(&memcg->res, RES_USAGE);
                /* Usage is reduced ? */
                if (curusage >= oldusage)
                        retry_count--;
                else
                        oldusage = curusage;
        }
        if (!ret && enlarge)
                memcg_oom_recover(memcg);

        return ret;
}

static int mem_cgroup_resize_memsw_limit(struct mem_cgroup *memcg,
                                        unsigned long long val)
{
        int retry_count;
        u64 memlimit, memswlimit, oldusage, curusage;
        int children = mem_cgroup_count_children(memcg);
        int ret = -EBUSY;
        int enlarge = 0;

        /* see mem_cgroup_resize_res_limit */
        retry_count = children * MEM_CGROUP_RECLAIM_RETRIES;
        oldusage = res_counter_read_u64(&memcg->memsw, RES_USAGE);
        while (retry_count) {
                if (signal_pending(current)) {
                        ret = -EINTR;
                        break;
                }
                /*
                 * Rather than hide all in some function, I do this in
                 * open coded manner. You see what this really does.
                 * We have to guarantee memcg->res.limit <= memcg->memsw.limit.
                 */
                mutex_lock(&set_limit_mutex);
                memlimit = res_counter_read_u64(&memcg->res, RES_LIMIT);
                if (memlimit > val) {
                        ret = -EINVAL;
                        mutex_unlock(&set_limit_mutex);
                        break;
                }
                memswlimit = res_counter_read_u64(&memcg->memsw, RES_LIMIT);
                if (memswlimit < val)
                        enlarge = 1;
                ret = res_counter_set_limit(&memcg->memsw, val);
                if (!ret) {
                        if (memlimit == val)
                                memcg->memsw_is_minimum = true;
                        else
                                memcg->memsw_is_minimum = false;
                }
                mutex_unlock(&set_limit_mutex);

                if (!ret)
                        break;

                mem_cgroup_reclaim(memcg, GFP_KERNEL,
                                   MEM_CGROUP_RECLAIM_NOSWAP |
                                   MEM_CGROUP_RECLAIM_SHRINK);
                curusage = res_counter_read_u64(&memcg->memsw, RES_USAGE);
                /* Usage is reduced ? */
                if (curusage >= oldusage)
                        retry_count--;
                else
                        oldusage = curusage;
        }
        if (!ret && enlarge)
                memcg_oom_recover(memcg);
        return ret;
}

unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
                                            gfp_t gfp_mask,
                                            unsigned long *total_scanned)
{
        unsigned long nr_reclaimed = 0;
        struct mem_cgroup_per_zone *mz, *next_mz = NULL;
        unsigned long reclaimed;
        int loop = 0;
        struct mem_cgroup_tree_per_zone *mctz;
        unsigned long long excess;
        unsigned long nr_scanned;

        if (order > 0)
                return 0;

        mctz = soft_limit_tree_node_zone(zone_to_nid(zone), zone_idx(zone));
        /*
         * This loop can run a while, specially if mem_cgroup's continuously
         * keep exceeding their soft limit and putting the system under
         * pressure
         */
        do {
                if (next_mz)
                        mz = next_mz;
                else
                        mz = mem_cgroup_largest_soft_limit_node(mctz);
                if (!mz)
                        break;

                nr_scanned = 0;
                reclaimed = mem_cgroup_soft_reclaim(mz->memcg, zone,
                                                    gfp_mask, &nr_scanned);
                nr_reclaimed += reclaimed;
                *total_scanned += nr_scanned;
                spin_lock(&mctz->lock);

                /*
                 * If we failed to reclaim anything from this memory cgroup
                 * it is time to move on to the next cgroup
                 */
                next_mz = NULL;
                if (!reclaimed) {
                        do {
                                /*
                                 * Loop until we find yet another one.
                                 *
                                 * By the time we get the soft_limit lock
                                 * again, someone might have aded the
                                 * group back on the RB tree. Iterate to
                                 * make sure we get a different mem.
                                 * mem_cgroup_largest_soft_limit_node returns
                                 * NULL if no other cgroup is present on
                                 * the tree
                                 */
                                next_mz =
                                __mem_cgroup_largest_soft_limit_node(mctz);
                                if (next_mz == mz)
                                        css_put(&next_mz->memcg->css);
                                else /* next_mz == NULL or other memcg */
                                        break;
                        } while (1);
                }
                __mem_cgroup_remove_exceeded(mz->memcg, mz, mctz);
                excess = res_counter_soft_limit_excess(&mz->memcg->res);
                /*
                 * One school of thought says that we should not add
                 * back the node to the tree if reclaim returns 0.
                 * But our reclaim could return 0, simply because due
                 * to priority we are exposing a smaller subset of
                 * memory to reclaim from. Consider this as a longer
                 * term TODO.
                 */
                /* If excess == 0, no tree ops */
                __mem_cgroup_insert_exceeded(mz->memcg, mz, mctz, excess);
                spin_unlock(&mctz->lock);
                css_put(&mz->memcg->css);
                loop++;
                /*
                 * Could not reclaim anything and there are no more
                 * mem cgroups to try or we seem to be looping without
                 * reclaiming anything.
                 */
                if (!nr_reclaimed &&
                        (next_mz == NULL ||
                        loop > MEM_CGROUP_MAX_SOFT_LIMIT_RECLAIM_LOOPS))
                        break;
        } while (!nr_reclaimed);
        if (next_mz)
                css_put(&next_mz->memcg->css);
        return nr_reclaimed;
}

/*
 * Traverse a specified page_cgroup list and try to drop them all.  This doesn't
 * reclaim the pages page themselves - it just removes the page_cgroups.
 * Returns true if some page_cgroups were not freed, indicating that the caller
 * must retry this operation.
 */
static bool mem_cgroup_force_empty_list(struct mem_cgroup *memcg,
                                int node, int zid, enum lru_list lru)
{
        struct lruvec *lruvec;
        unsigned long flags, loop;
        struct list_head *list;
        struct page *busy;
        struct zone *zone;

        zone = &NODE_DATA(node)->node_zones[zid];
        lruvec = mem_cgroup_zone_lruvec(zone, memcg);
        list = &lruvec->lists[lru];

        loop = mem_cgroup_get_lru_size(lruvec, lru);
        /* give some margin against EBUSY etc...*/
        loop += 256;
        busy = NULL;
        while (loop--) {
                struct page_cgroup *pc;
                struct page *page;

                spin_lock_irqsave(&zone->lru_lock, flags);
                if (list_empty(list)) {
                        spin_unlock_irqrestore(&zone->lru_lock, flags);
                        break;
                }
                page = list_entry(list->prev, struct page, lru);
                if (busy == page) {
                        list_move(&page->lru, list);
                        busy = NULL;
                        spin_unlock_irqrestore(&zone->lru_lock, flags);
                        continue;
                }
                spin_unlock_irqrestore(&zone->lru_lock, flags);

                pc = lookup_page_cgroup(page);

                if (mem_cgroup_move_parent(page, pc, memcg)) {
                        /* found lock contention or "pc" is obsolete. */
                        busy = page;
                        cond_resched();
                } else
                        busy = NULL;
        }
        return !list_empty(list);
}

/*
 * make mem_cgroup's charge to be 0 if there is no task.
 * This enables deleting this mem_cgroup.
 */
static int mem_cgroup_force_empty(struct mem_cgroup *memcg, bool free_all)
{
        int ret;
        int node, zid, shrink;
        int nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
        struct cgroup *cgrp = memcg->css.cgroup;

        css_get(&memcg->css);

        shrink = 0;
        /* should free all ? */
        if (free_all)
                goto try_to_free;
move_account:
        do {
                ret = -EBUSY;
                if (cgroup_task_count(cgrp) || !list_empty(&cgrp->children))
                        goto out;
                /* This is for making all *used* pages to be on LRU. */
                lru_add_drain_all();
                drain_all_stock_sync(memcg);
                ret = 0;
                mem_cgroup_start_move(memcg);
                for_each_node_state(node, N_HIGH_MEMORY) {
                        for (zid = 0; !ret && zid < MAX_NR_ZONES; zid++) {
                                enum lru_list lru;
                                for_each_lru(lru) {
                                        ret = mem_cgroup_force_empty_list(memcg,
                                                        node, zid, lru);
                                        if (ret)
                                                break;
                                }
                        }
                        if (ret)
                                break;
                }
                mem_cgroup_end_move(memcg);
                memcg_oom_recover(memcg);
                cond_resched();
        /* "ret" should also be checked to ensure all lists are empty. */
        } while (res_counter_read_u64(&memcg->res, RES_USAGE) > 0 || ret);
out:
        css_put(&memcg->css);
        return ret;

try_to_free:
        /* returns EBUSY if there is a task or if we come here twice. */
        if (cgroup_task_count(cgrp) || !list_empty(&cgrp->children) || shrink) {
                ret = -EBUSY;
                goto out;
        }
        /* we call try-to-free pages for make this cgroup empty */
        lru_add_drain_all();
        /* try to free all pages in this cgroup */
        shrink = 1;
        while (nr_retries && res_counter_read_u64(&memcg->res, RES_USAGE) > 0) {
                int progress;

                if (signal_pending(current)) {
                        ret = -EINTR;
                        goto out;
                }
                progress = try_to_free_mem_cgroup_pages(memcg, GFP_KERNEL,
                                                false);
                if (!progress) {
                        nr_retries--;
                        /* maybe some writeback is necessary */
                        congestion_wait(BLK_RW_ASYNC, HZ/10);
                }

        }
        lru_add_drain();
        /* try move_account...there may be some *locked* pages. */
        goto move_account;
}

static int mem_cgroup_force_empty_write(struct cgroup *cont, unsigned int event)
{
        return mem_cgroup_force_empty(mem_cgroup_from_cont(cont), true);
}


static u64 mem_cgroup_hierarchy_read(struct cgroup *cont, struct cftype *cft)
{
        return mem_cgroup_from_cont(cont)->use_hierarchy;
}

static int mem_cgroup_hierarchy_write(struct cgroup *cont, struct cftype *cft,
                                        u64 val)
{
        int retval = 0;
        struct mem_cgroup *memcg = mem_cgroup_from_cont(cont);
        struct cgroup *parent = cont->parent;
        struct mem_cgroup *parent_memcg = NULL;

        if (parent)
                parent_memcg = mem_cgroup_from_cont(parent);

        cgroup_lock();

        if (memcg->use_hierarchy == val)
                goto out;

        /*
         * If parent's use_hierarchy is set, we can't make any modifications
         * in the child subtrees. If it is unset, then the change can
         * occur, provided the current cgroup has no children.
         *
         * For the root cgroup, parent_mem is NULL, we allow value to be
         * set if there are no children.
         */
        if ((!parent_memcg || !parent_memcg->use_hierarchy) &&
                                (val == 1 || val == 0)) {
                if (list_empty(&cont->children))
                        memcg->use_hierarchy = val;
                else
                        retval = -EBUSY;
        } else
                retval = -EINVAL;

out:
        cgroup_unlock();

        return retval;
}


static unsigned long mem_cgroup_recursive_stat(struct mem_cgroup *memcg,
                                               enum mem_cgroup_stat_index idx)
{
        struct mem_cgroup *iter;
        long val = 0;

        /* Per-cpu values can be negative, use a signed accumulator */
        for_each_mem_cgroup_tree(iter, memcg)
                val += mem_cgroup_read_stat(iter, idx);

        if (val < 0) /* race ? */
                val = 0;
        return val;
}

static inline u64 mem_cgroup_usage(struct mem_cgroup *memcg, bool swap)
{
        u64 val;

        if (!mem_cgroup_is_root(memcg)) {
                if (!swap)
                        return res_counter_read_u64(&memcg->res, RES_USAGE);
                else
                        return res_counter_read_u64(&memcg->memsw, RES_USAGE);
        }

        val = mem_cgroup_recursive_stat(memcg, MEM_CGROUP_STAT_CACHE);
        val += mem_cgroup_recursive_stat(memcg, MEM_CGROUP_STAT_RSS);

        if (swap)
                val += mem_cgroup_recursive_stat(memcg, MEM_CGROUP_STAT_SWAP);

        return val << PAGE_SHIFT;
}

static ssize_t mem_cgroup_read(struct cgroup *cont, struct cftype *cft,
                               struct file *file, char __user *buf,
                               size_t nbytes, loff_t *ppos)
{
        struct mem_cgroup *memcg = mem_cgroup_from_cont(cont);
        char str[64];
        u64 val;
        int type, name, len;

        type = MEMFILE_TYPE(cft->private);
        name = MEMFILE_ATTR(cft->private);

        if (!do_swap_account && type == _MEMSWAP)
                return -EOPNOTSUPP;

        switch (type) {
        case _MEM:
                if (name == RES_USAGE)
                        val = mem_cgroup_usage(memcg, false);
                else
                        val = res_counter_read_u64(&memcg->res, name);
                break;
        case _MEMSWAP:
                if (name == RES_USAGE)
                        val = mem_cgroup_usage(memcg, true);
                else
                        val = res_counter_read_u64(&memcg->memsw, name);
                break;
        default:
                BUG();
        }

        len = scnprintf(str, sizeof(str), "%llu\n", (unsigned long long)val);
        return simple_read_from_buffer(buf, nbytes, ppos, str, len);
}
/*
 * The user of this function is...
 * RES_LIMIT.
 */
static int mem_cgroup_write(struct cgroup *cont, struct cftype *cft,
                            const char *buffer)
{
        struct mem_cgroup *memcg = mem_cgroup_from_cont(cont);
        int type, name;
        unsigned long long val;
        int ret;

        type = MEMFILE_TYPE(cft->private);
        name = MEMFILE_ATTR(cft->private);

        if (!do_swap_account && type == _MEMSWAP)
                return -EOPNOTSUPP;

        switch (name) {
        case RES_LIMIT:
                if (mem_cgroup_is_root(memcg)) { /* Can't set limit on root */
                        ret = -EINVAL;
                        break;
                }
                /* This function does all necessary parse...reuse it */
                ret = res_counter_memparse_write_strategy(buffer, &val);
                if (ret)
                        break;
                if (type == _MEM)
                        ret = mem_cgroup_resize_limit(memcg, val);
                else
                        ret = mem_cgroup_resize_memsw_limit(memcg, val);