/*
 * zcache.c
 *
 * Copyright (c) 2010,2011, Dan Magenheimer, Oracle Corp.
 * Copyright (c) 2010,2011, Nitin Gupta
 *
 * Zcache provides an in-kernel "host implementation" for transcendent memory
 * and, thus indirectly, for cleancache and frontswap.  Zcache includes two
 * page-accessible memory [1] interfaces, both utilizing lzo1x compression:
 * 1) "compression buddies" ("zbud") is used for ephemeral pages
 * 2) xvmalloc is used for persistent pages.
 * Xvmalloc (based on the TLSF allocator) has very low fragmentation
 * so maximizes space efficiency, while zbud allows pairs (and potentially,
 * in the future, more than a pair of) compressed pages to be closely linked
 * so that reclaiming can be done via the kernel's physical-page-oriented
 * "shrinker" interface.
 *
 * [1] For a definition of page-accessible memory (aka PAM), see:
 *   http://marc.info/?l=linux-mm&m=127811271605009
 */

#include <linux/cpu.h>
#include <linux/highmem.h>
#include <linux/list.h>
#include <linux/lzo.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/types.h>
#include <linux/atomic.h>
#include "tmem.h"

#include "../zram/xvmalloc.h" /* if built in drivers/staging */

#if (!defined(CONFIG_CLEANCACHE) && !defined(CONFIG_FRONTSWAP))
#error "zcache is useless without CONFIG_CLEANCACHE or CONFIG_FRONTSWAP"
#endif
#ifdef CONFIG_CLEANCACHE
#include <linux/cleancache.h>
#endif
#ifdef CONFIG_FRONTSWAP
#include <linux/frontswap.h>
#endif

#if 0
/* this is more aggressive but may cause other problems? */
#define ZCACHE_GFP_MASK (GFP_ATOMIC | __GFP_NORETRY | __GFP_NOWARN)
#else
#define ZCACHE_GFP_MASK \
        (__GFP_FS | __GFP_NORETRY | __GFP_NOWARN | __GFP_NOMEMALLOC)
#endif

/**********
 * Compression buddies ("zbud") provides for packing two (or, possibly
 * in the future, more) compressed ephemeral pages into a single "raw"
 * (physical) page and tracking them with data structures so that
 * the raw pages can be easily reclaimed.
 *
 * A zbud page ("zbpg") is an aligned page containing a list_head,
 * a lock, and two "zbud headers".  The remainder of the physical
 * page is divided up into aligned 64-byte "chunks" which contain
 * the compressed data for zero, one, or two zbuds.  Each zbpg
 * resides on: (1) an "unused list" if it has no zbuds; (2) a
 * "buddied" list if it is fully populated  with two zbuds; or
 * (3) one of PAGE_SIZE/64 "unbuddied" lists indexed by how many chunks
 * the one unbuddied zbud uses.  The data inside a zbpg cannot be
 * read or written unless the zbpg's lock is held.
 */

#define ZBH_SENTINEL  0x43214321
#define ZBPG_SENTINEL  0xdeadbeef

#define ZBUD_MAX_BUDS 2

struct zbud_hdr {
        uint32_t pool_id;
        struct tmem_oid oid;
        uint32_t index;
        uint16_t size; /* compressed size in bytes, zero means unused */
        DECL_SENTINEL
};

struct zbud_page {
        struct list_head bud_list;
        spinlock_t lock;
        struct zbud_hdr buddy[ZBUD_MAX_BUDS];
        DECL_SENTINEL
        /* followed by NUM_CHUNK aligned CHUNK_SIZE-byte chunks */
};

#define CHUNK_SHIFT     6
#define CHUNK_SIZE      (1 << CHUNK_SHIFT)
#define CHUNK_MASK      (~(CHUNK_SIZE-1))
#define NCHUNKS         (((PAGE_SIZE - sizeof(struct zbud_page)) & \
                                CHUNK_MASK) >> CHUNK_SHIFT)
#define MAX_CHUNK       (NCHUNKS-1)

static struct {
        struct list_head list;
        unsigned count;
} zbud_unbuddied[NCHUNKS];
/* list N contains pages with N chunks USED and NCHUNKS-N unused */
/* element 0 is never used but optimizing that isn't worth it */
static unsigned long zbud_cumul_chunk_counts[NCHUNKS];

struct list_head zbud_buddied_list;
static unsigned long zcache_zbud_buddied_count;

/* protects the buddied list and all unbuddied lists */
static DEFINE_SPINLOCK(zbud_budlists_spinlock);

static LIST_HEAD(zbpg_unused_list);
static unsigned long zcache_zbpg_unused_list_count;

/* protects the unused page list */
static DEFINE_SPINLOCK(zbpg_unused_list_spinlock);

static atomic_t zcache_zbud_curr_raw_pages;
static atomic_t zcache_zbud_curr_zpages;
static unsigned long zcache_zbud_curr_zbytes;
static unsigned long zcache_zbud_cumul_zpages;
static unsigned long zcache_zbud_cumul_zbytes;
static unsigned long zcache_compress_poor;

/* forward references */
static void *zcache_get_free_page(void);
static void zcache_free_page(void *p);

/*
 * zbud helper functions
 */

static inline unsigned zbud_max_buddy_size(void)
{
        return MAX_CHUNK << CHUNK_SHIFT;
}

static inline unsigned zbud_size_to_chunks(unsigned size)
{
        BUG_ON(size == 0 || size > zbud_max_buddy_size());
        return (size + CHUNK_SIZE - 1) >> CHUNK_SHIFT;
}

static inline int zbud_budnum(struct zbud_hdr *zh)
{
        unsigned offset = (unsigned long)zh & (PAGE_SIZE - 1);
        struct zbud_page *zbpg = NULL;
        unsigned budnum = -1U;
        int i;

        for (i = 0; i < ZBUD_MAX_BUDS; i++)
                if (offset == offsetof(typeof(*zbpg), buddy[i])) {
                        budnum = i;
                        break;
                }
        BUG_ON(budnum == -1U);
        return budnum;
}

static char *zbud_data(struct zbud_hdr *zh, unsigned size)
{
        struct zbud_page *zbpg;
        char *p;
        unsigned budnum;

        ASSERT_SENTINEL(zh, ZBH);
        budnum = zbud_budnum(zh);
        BUG_ON(size == 0 || size > zbud_max_buddy_size());
        zbpg = container_of(zh, struct zbud_page, buddy[budnum]);
        ASSERT_SPINLOCK(&zbpg->lock);
        p = (char *)zbpg;
        if (budnum == 0)
                p += ((sizeof(struct zbud_page) + CHUNK_SIZE - 1) &
                                                        CHUNK_MASK);
        else if (budnum == 1)
                p += PAGE_SIZE - ((size + CHUNK_SIZE - 1) & CHUNK_MASK);
        return p;
}

/*
 * zbud raw page management
 */

static struct zbud_page *zbud_alloc_raw_page(void)
{
        struct zbud_page *zbpg = NULL;
        struct zbud_hdr *zh0, *zh1;
        bool recycled = 0;

        /* if any pages on the zbpg list, use one */
        spin_lock(&zbpg_unused_list_spinlock);
        if (!list_empty(&zbpg_unused_list)) {
                zbpg = list_first_entry(&zbpg_unused_list,
                                struct zbud_page, bud_list);
                list_del_init(&zbpg->bud_list);
                zcache_zbpg_unused_list_count--;
                recycled = 1;
        }
        spin_unlock(&zbpg_unused_list_spinlock);
        if (zbpg == NULL)
                /* none on zbpg list, try to get a kernel page */
                zbpg = zcache_get_free_page();
        if (likely(zbpg != NULL)) {
                INIT_LIST_HEAD(&zbpg->bud_list);
                zh0 = &zbpg->buddy[0]; zh1 = &zbpg->buddy[1];
                spin_lock_init(&zbpg->lock);
                if (recycled) {
                        ASSERT_INVERTED_SENTINEL(zbpg, ZBPG);
                        SET_SENTINEL(zbpg, ZBPG);
                        BUG_ON(zh0->size != 0 || tmem_oid_valid(&zh0->oid));
                        BUG_ON(zh1->size != 0 || tmem_oid_valid(&zh1->oid));
                } else {
                        atomic_inc(&zcache_zbud_curr_raw_pages);
                        INIT_LIST_HEAD(&zbpg->bud_list);
                        SET_SENTINEL(zbpg, ZBPG);
                        zh0->size = 0; zh1->size = 0;
                        tmem_oid_set_invalid(&zh0->oid);
                        tmem_oid_set_invalid(&zh1->oid);
                }
        }
        return zbpg;
}

static void zbud_free_raw_page(struct zbud_page *zbpg)
{
        struct zbud_hdr *zh0 = &zbpg->buddy[0], *zh1 = &zbpg->buddy[1];

        ASSERT_SENTINEL(zbpg, ZBPG);
        BUG_ON(!list_empty(&zbpg->bud_list));
        ASSERT_SPINLOCK(&zbpg->lock);
        BUG_ON(zh0->size != 0 || tmem_oid_valid(&zh0->oid));
        BUG_ON(zh1->size != 0 || tmem_oid_valid(&zh1->oid));
        INVERT_SENTINEL(zbpg, ZBPG);
        spin_unlock(&zbpg->lock);
        spin_lock(&zbpg_unused_list_spinlock);
        list_add(&zbpg->bud_list, &zbpg_unused_list);
        zcache_zbpg_unused_list_count++;
        spin_unlock(&zbpg_unused_list_spinlock);
}

/*
 * core zbud handling routines
 */

static unsigned zbud_free(struct zbud_hdr *zh)
{
        unsigned size;

        ASSERT_SENTINEL(zh, ZBH);
        BUG_ON(!tmem_oid_valid(&zh->oid));
        size = zh->size;
        BUG_ON(zh->size == 0 || zh->size > zbud_max_buddy_size());
        zh->size = 0;
        tmem_oid_set_invalid(&zh->oid);
        INVERT_SENTINEL(zh, ZBH);
        zcache_zbud_curr_zbytes -= size;
        atomic_dec(&zcache_zbud_curr_zpages);
        return size;
}

static void zbud_free_and_delist(struct zbud_hdr *zh)
{
        unsigned chunks;
        struct zbud_hdr *zh_other;
        unsigned budnum = zbud_budnum(zh), size;
        struct zbud_page *zbpg =
                container_of(zh, struct zbud_page, buddy[budnum]);

        spin_lock(&zbpg->lock);
        if (list_empty(&zbpg->bud_list)) {
                /* ignore zombie page... see zbud_evict_pages() */
                spin_unlock(&zbpg->lock);
                return;
        }
        size = zbud_free(zh);
        ASSERT_SPINLOCK(&zbpg->lock);
        zh_other = &zbpg->buddy[(budnum == 0) ? 1 : 0];
        if (zh_other->size == 0) { /* was unbuddied: unlist and free */
                chunks = zbud_size_to_chunks(size) ;
                spin_lock(&zbud_budlists_spinlock);
                BUG_ON(list_empty(&zbud_unbuddied[chunks].list));
                list_del_init(&zbpg->bud_list);
                zbud_unbuddied[chunks].count--;
                spin_unlock(&zbud_budlists_spinlock);
                zbud_free_raw_page(zbpg);
        } else { /* was buddied: move remaining buddy to unbuddied list */
                chunks = zbud_size_to_chunks(zh_other->size) ;
                spin_lock(&zbud_budlists_spinlock);
                list_del_init(&zbpg->bud_list);
                zcache_zbud_buddied_count--;
                list_add_tail(&zbpg->bud_list, &zbud_unbuddied[chunks].list);
                zbud_unbuddied[chunks].count++;
                spin_unlock(&zbud_budlists_spinlock);
                spin_unlock(&zbpg->lock);
        }
}

static struct zbud_hdr *zbud_create(uint32_t pool_id, struct tmem_oid *oid,
                                        uint32_t index, struct page *page,
                                        void *cdata, unsigned size)
{
        struct zbud_hdr *zh0, *zh1, *zh = NULL;
        struct zbud_page *zbpg = NULL, *ztmp;
        unsigned nchunks;
        char *to;
        int i, found_good_buddy = 0;

        nchunks = zbud_size_to_chunks(size) ;
        for (i = MAX_CHUNK - nchunks + 1; i > 0; i--) {
                spin_lock(&zbud_budlists_spinlock);
                if (!list_empty(&zbud_unbuddied[i].list)) {
                        list_for_each_entry_safe(zbpg, ztmp,
                                    &zbud_unbuddied[i].list, bud_list) {
                                if (spin_trylock(&zbpg->lock)) {
                                        found_good_buddy = i;
                                        goto found_unbuddied;
                                }
                        }
                }
                spin_unlock(&zbud_budlists_spinlock);
        }
        /* didn't find a good buddy, try allocating a new page */
        zbpg = zbud_alloc_raw_page();
        if (unlikely(zbpg == NULL))
                goto out;
        /* ok, have a page, now compress the data before taking locks */
        spin_lock(&zbpg->lock);
        spin_lock(&zbud_budlists_spinlock);
        list_add_tail(&zbpg->bud_list, &zbud_unbuddied[nchunks].list);
        zbud_unbuddied[nchunks].count++;
        zh = &zbpg->buddy[0];
        goto init_zh;

found_unbuddied:
        ASSERT_SPINLOCK(&zbpg->lock);
        zh0 = &zbpg->buddy[0]; zh1 = &zbpg->buddy[1];
        BUG_ON(!((zh0->size == 0) ^ (zh1->size == 0)));
        if (zh0->size != 0) { /* buddy0 in use, buddy1 is vacant */
                ASSERT_SENTINEL(zh0, ZBH);
                zh = zh1;
        } else if (zh1->size != 0) { /* buddy1 in use, buddy0 is vacant */
                ASSERT_SENTINEL(zh1, ZBH);
                zh = zh0;
        } else
                BUG();
        list_del_init(&zbpg->bud_list);
        zbud_unbuddied[found_good_buddy].count--;
        list_add_tail(&zbpg->bud_list, &zbud_buddied_list);
        zcache_zbud_buddied_count++;

init_zh:
        SET_SENTINEL(zh, ZBH);
        zh->size = size;
        zh->index = index;
        zh->oid = *oid;
        zh->pool_id = pool_id;
        /* can wait to copy the data until the list locks are dropped */
        spin_unlock(&zbud_budlists_spinlock);

        to = zbud_data(zh, size);
        memcpy(to, cdata, size);
        spin_unlock(&zbpg->lock);
        zbud_cumul_chunk_counts[nchunks]++;
        atomic_inc(&zcache_zbud_curr_zpages);
        zcache_zbud_cumul_zpages++;
        zcache_zbud_curr_zbytes += size;
        zcache_zbud_cumul_zbytes += size;
out:
        return zh;
}

static int zbud_decompress(struct page *page, struct zbud_hdr *zh)
{
        struct zbud_page *zbpg;
        unsigned budnum = zbud_budnum(zh);
        size_t out_len = PAGE_SIZE;
        char *to_va, *from_va;
        unsigned size;
        int ret = 0;

        zbpg = container_of(zh, struct zbud_page, buddy[budnum]);
        spin_lock(&zbpg->lock);
        if (list_empty(&zbpg->bud_list)) {
                /* ignore zombie page... see zbud_evict_pages() */
                ret = -EINVAL;
                goto out;
        }
        ASSERT_SENTINEL(zh, ZBH);
        BUG_ON(zh->size == 0 || zh->size > zbud_max_buddy_size());
        to_va = kmap_atomic(page, KM_USER0);
        size = zh->size;
        from_va = zbud_data(zh, size);
        ret = lzo1x_decompress_safe(from_va, size, to_va, &out_len);
        BUG_ON(ret != LZO_E_OK);
        BUG_ON(out_len != PAGE_SIZE);
        kunmap_atomic(to_va, KM_USER0);
out:
        spin_unlock(&zbpg->lock);
        return ret;
}

/*
 * The following routines handle shrinking of ephemeral pages by evicting
 * pages "least valuable" first.
 */

static unsigned long zcache_evicted_raw_pages;
static unsigned long zcache_evicted_buddied_pages;
static unsigned long zcache_evicted_unbuddied_pages;

static struct tmem_pool *zcache_get_pool_by_id(uint32_t poolid);
static void zcache_put_pool(struct tmem_pool *pool);

/*
 * Flush and free all zbuds in a zbpg, then free the pageframe
 */
static void zbud_evict_zbpg(struct zbud_page *zbpg)
{
        struct zbud_hdr *zh;
        int i, j;
        uint32_t pool_id[ZBUD_MAX_BUDS], index[ZBUD_MAX_BUDS];
        struct tmem_oid oid[ZBUD_MAX_BUDS];
        struct tmem_pool *pool;

        ASSERT_SPINLOCK(&zbpg->lock);
        BUG_ON(!list_empty(&zbpg->bud_list));
        for (i = 0, j = 0; i < ZBUD_MAX_BUDS; i++) {
                zh = &zbpg->buddy[i];
                if (zh->size) {
                        pool_id[j] = zh->pool_id;
                        oid[j] = zh->oid;
                        index[j] = zh->index;
                        j++;
                        zbud_free(zh);
                }
        }
        spin_unlock(&zbpg->lock);
        for (i = 0; i < j; i++) {
                pool = zcache_get_pool_by_id(pool_id[i]);
                if (pool != NULL) {
                        tmem_flush_page(pool, &oid[i], index[i]);
                        zcache_put_pool(pool);
                }
        }
        ASSERT_SENTINEL(zbpg, ZBPG);
        spin_lock(&zbpg->lock);
        zbud_free_raw_page(zbpg);
}

/*
 * Free nr pages.  This code is funky because we want to hold the locks
 * protecting various lists for as short a time as possible, and in some
 * circumstances the list may change asynchronously when the list lock is
 * not held.  In some cases we also trylock not only to avoid waiting on a
 * page in use by another cpu, but also to avoid potential deadlock due to
 * lock inversion.
 */
static void zbud_evict_pages(int nr)
{
        struct zbud_page *zbpg;
        int i;

        /* first try freeing any pages on unused list */
retry_unused_list:
        spin_lock_bh(&zbpg_unused_list_spinlock);
        if (!list_empty(&zbpg_unused_list)) {
                /* can't walk list here, since it may change when unlocked */
                zbpg = list_first_entry(&zbpg_unused_list,
                                struct zbud_page, bud_list);
                list_del_init(&zbpg->bud_list);
                zcache_zbpg_unused_list_count--;
                atomic_dec(&zcache_zbud_curr_raw_pages);
                spin_unlock_bh(&zbpg_unused_list_spinlock);
                zcache_free_page(zbpg);
                zcache_evicted_raw_pages++;
                if (--nr <= 0)
                        goto out;
                goto retry_unused_list;
        }
        spin_unlock_bh(&zbpg_unused_list_spinlock);

        /* now try freeing unbuddied pages, starting with least space avail */
        for (i = 0; i < MAX_CHUNK; i++) {
retry_unbud_list_i:
                spin_lock_bh(&zbud_budlists_spinlock);
                if (list_empty(&zbud_unbuddied[i].list)) {
                        spin_unlock_bh(&zbud_budlists_spinlock);
                        continue;
                }
                list_for_each_entry(zbpg, &zbud_unbuddied[i].list, bud_list) {
                        if (unlikely(!spin_trylock(&zbpg->lock)))
                                continue;
                        list_del_init(&zbpg->bud_list);
                        zbud_unbuddied[i].count--;
                        spin_unlock(&zbud_budlists_spinlock);
                        zcache_evicted_unbuddied_pages++;
                        /* want budlists unlocked when doing zbpg eviction */
                        zbud_evict_zbpg(zbpg);
                        local_bh_enable();
                        if (--nr <= 0)
                                goto out;
                        goto retry_unbud_list_i;
                }
                spin_unlock_bh(&zbud_budlists_spinlock);
        }

        /* as a last resort, free buddied pages */
retry_bud_list:
        spin_lock_bh(&zbud_budlists_spinlock);
        if (list_empty(&zbud_buddied_list)) {
                spin_unlock_bh(&zbud_budlists_spinlock);
                goto out;
        }
        list_for_each_entry(zbpg, &zbud_buddied_list, bud_list) {
                if (unlikely(!spin_trylock(&zbpg->lock)))
                        continue;
                list_del_init(&zbpg->bud_list);
                zcache_zbud_buddied_count--;
                spin_unlock(&zbud_budlists_spinlock);
                zcache_evicted_buddied_pages++;
                /* want budlists unlocked when doing zbpg eviction */
                zbud_evict_zbpg(zbpg);
                local_bh_enable();
                if (--nr <= 0)
                        goto out;
                goto retry_bud_list;
        }
        spin_unlock_bh(&zbud_budlists_spinlock);
out:
        return;
}

static void zbud_init(void)
{
        int i;

        INIT_LIST_HEAD(&zbud_buddied_list);
        zcache_zbud_buddied_count = 0;
        for (i = 0; i < NCHUNKS; i++) {
                INIT_LIST_HEAD(&zbud_unbuddied[i].list);
                zbud_unbuddied[i].count = 0;
        }
}

#ifdef CONFIG_SYSFS
/*
 * These sysfs routines show a nice distribution of how many zbpg's are
 * currently (and have ever been placed) in each unbuddied list.  It's fun
 * to watch but can probably go away before final merge.
 */
static int zbud_show_unbuddied_list_counts(char *buf)
{
        int i;
        char *p = buf;

        for (i = 0; i < NCHUNKS - 1; i++)
                p += sprintf(p, "%u ", zbud_unbuddied[i].count);
        p += sprintf(p, "%d\n", zbud_unbuddied[i].count);
        return p - buf;
}

static int zbud_show_cumul_chunk_counts(char *buf)
{
        unsigned long i, chunks = 0, total_chunks = 0, sum_total_chunks = 0;
        unsigned long total_chunks_lte_21 = 0, total_chunks_lte_32 = 0;
        unsigned long total_chunks_lte_42 = 0;
        char *p = buf;

        for (i = 0; i < NCHUNKS; i++) {
                p += sprintf(p, "%lu ", zbud_cumul_chunk_counts[i]);
                chunks += zbud_cumul_chunk_counts[i];
                total_chunks += zbud_cumul_chunk_counts[i];
                sum_total_chunks += i * zbud_cumul_chunk_counts[i];
                if (i == 21)
                        total_chunks_lte_21 = total_chunks;
                if (i == 32)
                        total_chunks_lte_32 = total_chunks;
                if (i == 42)
                        total_chunks_lte_42 = total_chunks;
        }
        p += sprintf(p, "<=21:%lu <=32:%lu <=42:%lu, mean:%lu\n",
                total_chunks_lte_21, total_chunks_lte_32, total_chunks_lte_42,
                chunks == 0 ? 0 : sum_total_chunks / chunks);
        return p - buf;
}
#endif

/**********
 * This "zv" PAM implementation combines the TLSF-based xvMalloc
 * with lzo1x compression to maximize the amount of data that can
 * be packed into a physical page.
 *
 * Zv represents a PAM page with the index and object (plus a "size" value
 * necessary for decompression) immediately preceding the compressed data.
 */

#define ZVH_SENTINEL  0x43214321

struct zv_hdr {
        uint32_t pool_id;
        struct tmem_oid oid;
        uint32_t index;
        DECL_SENTINEL
};

static const int zv_max_page_size = (PAGE_SIZE / 8) * 7;

static struct zv_hdr *zv_create(struct xv_pool *xvpool, uint32_t pool_id,
                                struct tmem_oid *oid, uint32_t index,
                                void *cdata, unsigned clen)
{
        struct page *page;
        struct zv_hdr *zv = NULL;
        uint32_t offset;
        int ret;

        BUG_ON(!irqs_disabled());
        ret = xv_malloc(xvpool, clen + sizeof(struct zv_hdr),
                        &page, &offset, ZCACHE_GFP_MASK);
        if (unlikely(ret))
                goto out;
        zv = kmap_atomic(page, KM_USER0) + offset;
        zv->index = index;
        zv->oid = *oid;
        zv->pool_id = pool_id;
        SET_SENTINEL(zv, ZVH);
        memcpy((char *)zv + sizeof(struct zv_hdr), cdata, clen);
        kunmap_atomic(zv, KM_USER0);
out:
        return zv;
}

static void zv_free(struct xv_pool *xvpool, struct zv_hdr *zv)
{
        unsigned long flags;
        struct page *page;
        uint32_t offset;
        uint16_t size;

        ASSERT_SENTINEL(zv, ZVH);
        size = xv_get_object_size(zv) - sizeof(*zv);
        BUG_ON(size == 0 || size > zv_max_page_size);
        INVERT_SENTINEL(zv, ZVH);
        page = virt_to_page(zv);
        offset = (unsigned long)zv & ~PAGE_MASK;
        local_irq_save(flags);
        xv_free(xvpool, page, offset);
        local_irq_restore(flags);
}

static void zv_decompress(struct page *page, struct zv_hdr *zv)
{
        size_t clen = PAGE_SIZE;
        char *to_va;
        unsigned size;
        int ret;

        ASSERT_SENTINEL(zv, ZVH);
        size = xv_get_object_size(zv) - sizeof(*zv);
        BUG_ON(size == 0 || size > zv_max_page_size);
        to_va = kmap_atomic(page, KM_USER0);
        ret = lzo1x_decompress_safe((char *)zv + sizeof(*zv),
                                        size, to_va, &clen);
        kunmap_atomic(to_va, KM_USER0);
        BUG_ON(ret != LZO_E_OK);
        BUG_ON(clen != PAGE_SIZE);
}

/*
 * zcache core code starts here
 */

/* useful stats not collected by cleancache or frontswap */
static unsigned long zcache_flush_total;
static unsigned long zcache_flush_found;
static unsigned long zcache_flobj_total;
static unsigned long zcache_flobj_found;
static unsigned long zcache_failed_eph_puts;
static unsigned long zcache_failed_pers_puts;

#define MAX_POOLS_PER_CLIENT 16

static struct {
        struct tmem_pool *tmem_pools[MAX_POOLS_PER_CLIENT];
        struct xv_pool *xvpool;
} zcache_client;

/*
 * Tmem operations assume the poolid implies the invoking client.
 * Zcache only has one client (the kernel itself), so translate
 * the poolid into the tmem_pool allocated for it.  A KVM version
 * of zcache would have one client per guest and each client might
 * have a poolid==N.
 */
static struct tmem_pool *zcache_get_pool_by_id(uint32_t poolid)
{
        struct tmem_pool *pool = NULL;

        if (poolid >= 0) {
                pool = zcache_client.tmem_pools[poolid];
                if (pool != NULL)
                        atomic_inc(&pool->refcount);
        }
        return pool;
}

static void zcache_put_pool(struct tmem_pool *pool)
{
        if (pool != NULL)
                atomic_dec(&pool->refcount);
}

/* counters for debugging */
static unsigned long zcache_failed_get_free_pages;
static unsigned long zcache_failed_alloc;
static unsigned long zcache_put_to_flush;
static unsigned long zcache_aborted_preload;
static unsigned long zcache_aborted_shrink;

/*
 * Ensure that memory allocation requests in zcache don't result
 * in direct reclaim requests via the shrinker, which would cause
 * an infinite loop.  Maybe a GFP flag would be better?
 */
static DEFINE_SPINLOCK(zcache_direct_reclaim_lock);

/*
 * for now, used named slabs so can easily track usage; later can
 * either just use kmalloc, or perhaps add a slab-like allocator
 * to more carefully manage total memory utilization
 */
static struct kmem_cache *zcache_objnode_cache;
static struct kmem_cache *zcache_obj_cache;
static atomic_t zcache_curr_obj_count = ATOMIC_INIT(0);
static unsigned long zcache_curr_obj_count_max;
static atomic_t zcache_curr_objnode_count = ATOMIC_INIT(0);
static unsigned long zcache_curr_objnode_count_max;

/*
 * to avoid memory allocation recursion (e.g. due to direct reclaim), we
 * preload all necessary data structures so the hostops callbacks never
 * actually do a malloc
 */
struct zcache_preload {
        void *page;
        struct tmem_obj *obj;
        int nr;
        struct tmem_objnode *objnodes[OBJNODE_TREE_MAX_PATH];
};
static DEFINE_PER_CPU(struct zcache_preload, zcache_preloads) = { 0, };

static int zcache_do_preload(struct tmem_pool *pool)
{
        struct zcache_preload *kp;
        struct tmem_objnode *objnode;
        struct tmem_obj *obj;
        void *page;
        int ret = -ENOMEM;

        if (unlikely(zcache_objnode_cache == NULL))
                goto out;
        if (unlikely(zcache_obj_cache == NULL))
                goto out;
        if (!spin_trylock(&zcache_direct_reclaim_lock)) {
                zcache_aborted_preload++;
                goto out;
        }
        preempt_disable();
        kp = &__get_cpu_var(zcache_preloads);
        while (kp->nr < ARRAY_SIZE(kp->objnodes)) {
                preempt_enable_no_resched();
                objnode = kmem_cache_alloc(zcache_objnode_cache,
                                ZCACHE_GFP_MASK);
                if (unlikely(objnode == NULL)) {
                        zcache_failed_alloc++;
                        goto unlock_out;
                }
                preempt_disable();
                kp = &__get_cpu_var(zcache_preloads);
                if (kp->nr < ARRAY_SIZE(kp->objnodes))
                        kp->objnodes[kp->nr++] = objnode;
                else
                        kmem_cache_free(zcache_objnode_cache, objnode);
        }
        preempt_enable_no_resched();
        obj = kmem_cache_alloc(zcache_obj_cache, ZCACHE_GFP_MASK);
        if (unlikely(obj == NULL)) {
                zcache_failed_alloc++;
                goto unlock_out;
        }
        page = (void *)__get_free_page(ZCACHE_GFP_MASK);
        if (unlikely(page == NULL)) {
                zcache_failed_get_free_pages++;
                kmem_cache_free(zcache_obj_cache, obj);
                goto unlock_out;
        }
        preempt_disable();
        kp = &__get_cpu_var(zcache_preloads);
        if (kp->obj == NULL)
                kp->obj = obj;
        else
                kmem_cache_free(zcache_obj_cache, obj);
        if (kp->page == NULL)
                kp->page = page;
        else
                free_page((unsigned long)page);
        ret = 0;
unlock_out:
        spin_unlock(&zcache_direct_reclaim_lock);
out:
        return ret;
}

static void *zcache_get_free_page(void)
{
        struct zcache_preload *kp;
        void *page;

        kp = &__get_cpu_var(zcache_preloads);
        page = kp->page;
        BUG_ON(page == NULL);
        kp->page = NULL;
        return page;
}

static void zcache_free_page(void *p)
{
        free_page((unsigned long)p);
}

/*
 * zcache implementation for tmem host ops
 */

static struct tmem_objnode *zcache_objnode_alloc(struct tmem_pool *pool)
{
        struct tmem_objnode *objnode = NULL;
        unsigned long count;
        struct zcache_preload *kp;

        kp = &__get_cpu_var(zcache_preloads);
        if (kp->nr <= 0)
                goto out;
        objnode = kp->objnodes[kp->nr - 1];
        BUG_ON(objnode == NULL);
        kp->objnodes[kp->nr - 1] = NULL;
        kp->nr--;
        count = atomic_inc_return(&zcache_curr_objnode_count);
        if (count > zcache_curr_objnode_count_max)
                zcache_curr_objnode_count_max = count;
out:
        return objnode;
}

static void zcache_objnode_free(struct tmem_objnode *objnode,
                                        struct tmem_pool *pool)
{
        atomic_dec(&zcache_curr_objnode_count);
        BUG_ON(atomic_read(&zcache_curr_objnode_count) < 0);
        kmem_cache_free(zcache_objnode_cache, objnode);
}

static struct tmem_obj *zcache_obj_alloc(struct tmem_pool *pool)
{
        struct tmem_obj *obj = NULL;
        unsigned long count;
        struct zcache_preload *kp;

        kp = &__get_cpu_var(zcache_preloads);
        obj = kp->obj;
        BUG_ON(obj == NULL);
        kp->obj = NULL;
        count = atomic_inc_return(&zcache_curr_obj_count);
        if (count > zcache_curr_obj_count_max)
                zcache_curr_obj_count_max = count;
        return obj;
}

static void zcache_obj_free(struct tmem_obj *obj, struct tmem_pool *pool)
{
        atomic_dec(&zcache_curr_obj_count);
        BUG_ON(atomic_read(&zcache_curr_obj_count) < 0);
        kmem_cache_free(zcache_obj_cache, obj);
}

static struct tmem_hostops zcache_hostops = {
        .obj_alloc = zcache_obj_alloc,
        .obj_free = zcache_obj_free,
        .objnode_alloc = zcache_objnode_alloc,
        .objnode_free = zcache_objnode_free,
};

/*
 * zcache implementations for PAM page descriptor ops
 */

static atomic_t zcache_curr_eph_pampd_count = ATOMIC_INIT(0);
static unsigned long zcache_curr_eph_pampd_count_max;
static atomic_t zcache_curr_pers_pampd_count = ATOMIC_INIT(0);
static unsigned long zcache_curr_pers_pampd_count_max;

/* forward reference */
static int zcache_compress(struct page *from, void **out_va, size_t *out_len);

static void *zcache_pampd_create(struct tmem_pool *pool, struct tmem_oid *oid,
                                 uint32_t index, struct page *page)
{
        void *pampd = NULL, *cdata;
        size_t clen;
        int ret;
        bool ephemeral = is_ephemeral(pool);
        unsigned long count;

        if (ephemeral) {
                ret = zcache_compress(page, &cdata, &clen);
                if (ret == 0)

                        goto out;
                if (clen == 0 || clen > zbud_max_buddy_size()) {
                        zcache_compress_poor++;
                        goto out;
                }
                pampd = (void *)zbud_create(pool->pool_id, oid, index,
                                                page, cdata, clen);
                if (pampd != NULL) {
                        count = atomic_inc_return(&zcache_curr_eph_pampd_count);
                        if (count > zcache_curr_eph_pampd_count_max)
                                zcache_curr_eph_pampd_count_max = count;
                }
        } else {
                /*
                 * FIXME: This is all the "policy" there is for now.
                 * 3/4 totpages should allow ~37% of RAM to be filled with
                 * compressed frontswap pages
                 */
                if (atomic_read(&zcache_curr_pers_pampd_count) >
                                                        3 * totalram_pages / 4)
                        goto out;
                ret = zcache_compress(page, &cdata, &clen);
                if (ret == 0)
                        goto out;
                if (clen > zv_max_page_size) {
                        zcache_compress_poor++;
                        goto out;
                }
                pampd = (void *)zv_create(zcache_client.xvpool, pool->pool_id,
                                                oid, index, cdata, clen);
                if (pampd == NULL)
                        goto out;
                count = atomic_inc_return(&zcache_curr_pers_pampd_count);
                if (count > zcache_curr_pers_pampd_count_max)
                        zcache_curr_pers_pampd_count_max = count;
        }
out:
        return pampd;
}

/*
 * fill the pageframe corresponding to the struct page with the data
 * from the passed pampd
 */
static int zcache_pampd_get_data(struct page *page, void *pampd,
                                                struct tmem_pool *pool)
{
        int ret = 0;

        if (is_ephemeral(pool))
                ret = zbud_decompress(page, pampd);
        else
                zv_decompress(page, pampd);
        return ret;
}

/*
 * free the pampd and remove it from any zcache lists
 * pampd must no longer be pointed to from any tmem data structures!
 */
static void zcache_pampd_free(void *pampd, struct tmem_pool *pool)
{
        if (is_ephemeral(pool)) {
                zbud_free_and_delist((struct zbud_hdr *)pampd);
                atomic_dec(&zcache_curr_eph_pampd_count);
                BUG_ON(atomic_read(&zcache_curr_eph_pampd_count) < 0);
        } else {
                zv_free(zcache_client.xvpool, (struct zv_hdr *)pampd);
                atomic_dec(&zcache_curr_pers_pampd_count);
                BUG_ON(atomic_read(&zcache_curr_pers_pampd_count) < 0);
        }
}

static struct tmem_pamops zcache_pamops = {
        .create = zcache_pampd_create,
        .get_data = zcache_pampd_get_data,
        .free = zcache_pampd_free,
};

/*
 * zcache compression/decompression and related per-cpu stuff
 */

#define LZO_WORKMEM_BYTES LZO1X_1_MEM_COMPRESS

#define LZO_DSTMEM_PAGE_ORDER 1
static DEFINE_PER_CPU(unsigned char *, zcache_workmem);
static DEFINE_PER_CPU(unsigned char *, zcache_dstmem);

static int zcache_compress(struct page *from, void **out_va, size_t *out_len)
{
        int ret = 0;
        unsigned char *dmem = __get_cpu_var(zcache_dstmem);
        unsigned char *wmem = __get_cpu_var(zcache_workmem);
        char *from_va;

        BUG_ON(!irqs_disabled());
        if (unlikely(dmem == NULL || wmem == NULL))
                goto out;  /* no buffer, so can't compress */
        from_va = kmap_atomic(from, KM_USER0);
        mb();
        ret = lzo1x_1_compress(from_va, PAGE_SIZE, dmem, out_len, wmem);
        BUG_ON(ret != LZO_E_OK);
        *out_va = dmem;
        kunmap_atomic(from_va, KM_USER0);
        ret = 1;
out:
        return ret;
}


static int zcache_cpu_notifier(struct notifier_block *nb,
                                unsigned long action, void *pcpu)
{
        int cpu = (long)pcpu;
        struct zcache_preload *kp;

        switch (action) {
        case CPU_UP_PREPARE:
                per_cpu(zcache_dstmem, cpu) = (void *)__get_free_pages(
                        GFP_KERNEL | __GFP_REPEAT,
                        LZO_DSTMEM_PAGE_ORDER),
                per_cpu(zcache_workmem, cpu) =
                        kzalloc(LZO1X_MEM_COMPRESS,
                                GFP_KERNEL | __GFP_REPEAT);
                break;
        case CPU_DEAD:
        case CPU_UP_CANCELED:
                free_pages((unsigned long)per_cpu(zcache_dstmem, cpu),
                                LZO_DSTMEM_PAGE_ORDER);
                per_cpu(zcache_dstmem, cpu) = NULL;
                kfree(per_cpu(zcache_workmem, cpu));
                per_cpu(zcache_workmem, cpu) = NULL;
                kp = &per_cpu(zcache_preloads, cpu);
                while (kp->nr) {
                        kmem_cache_free(zcache_objnode_cache,
                                        kp->objnodes[kp->nr - 1]);
                        kp->objnodes[kp->nr - 1] = NULL;
                        kp->nr--;
                }
                kmem_cache_free(zcache_obj_cache, kp->obj);
                free_page((unsigned long)kp->page);
                break;
        default:
                break;
        }
        return NOTIFY_OK;
}

static struct notifier_block zcache_cpu_notifier_block = {
        .notifier_call = zcache_cpu_notifier
};

#ifdef CONFIG_SYSFS
#define ZCACHE_SYSFS_RO(_name) \
        static ssize_t zcache_##_name##_show(struct kobject *kobj, \
                                struct kobj_attribute *attr, char *buf) \
        { \
                return sprintf(buf, "%lu\n", zcache_##_name); \
        } \
        static struct kobj_attribute zcache_##_name##_attr = { \
                .attr = { .name = __stringify(_name), .mode = 0444 }, \
                .show = zcache_##_name##_show, \
        }

#define ZCACHE_SYSFS_RO_ATOMIC(_name) \
        static ssize_t zcache_##_name##_show(struct kobject *kobj, \
                                struct kobj_attribute *attr, char *buf) \
        { \
            return sprintf(buf, "%d\n", atomic_read(&zcache_##_name)); \
        } \
        static struct kobj_attribute zcache_##_name##_attr = { \
                .attr = { .name = __stringify(_name), .mode = 0444 }, \
                .show = zcache_##_name##_show, \
        }

#define ZCACHE_SYSFS_RO_CUSTOM(_name, _func) \
        static ssize_t zcache_##_name##_show(struct kobject *kobj, \
                                struct kobj_attribute *attr, char *buf) \
        { \
            return _func(buf); \
        } \
        static struct kobj_attribute zcache_##_name##_attr = { \
                .attr = { .name = __stringify(_name), .mode = 0444 }, \
                .show = zcache_##_name##_show, \
        }

ZCACHE_SYSFS_RO(curr_obj_count_max);
ZCACHE_SYSFS_RO(curr_objnode_count_max);
ZCACHE_SYSFS_RO(flush_total);
ZCACHE_SYSFS_RO(flush_found);
ZCACHE_SYSFS_RO(flobj_total);
ZCACHE_SYSFS_RO(flobj_found);
ZCACHE_SYSFS_RO(failed_eph_puts);
ZCACHE_SYSFS_RO(failed_pers_puts);
ZCACHE_SYSFS_RO(zbud_curr_zbytes);
ZCACHE_SYSFS_RO(zbud_cumul_zpages);
ZCACHE_SYSFS_RO(zbud_cumul_zbytes);
ZCACHE_SYSFS_RO(zbud_buddied_count);
ZCACHE_SYSFS_RO(zbpg_unused_list_count);
ZCACHE_SYSFS_RO(evicted_raw_pages);
ZCACHE_SYSFS_RO(evicted_unbuddied_pages);
ZCACHE_SYSFS_RO(evicted_buddied_pages);
ZCACHE_SYSFS_RO(failed_get_free_pages);
ZCACHE_SYSFS_RO(failed_alloc);
ZCACHE_SYSFS_RO(put_to_flush);
ZCACHE_SYSFS_RO(aborted_preload);
ZCACHE_SYSFS_RO(aborted_shrink);
ZCACHE_SYSFS_RO(compress_poor);
ZCACHE_SYSFS_RO_ATOMIC(zbud_curr_raw_pages);
ZCACHE_SYSFS_RO_ATOMIC(zbud_curr_zpages);
ZCACHE_SYSFS_RO_ATOMIC(curr_obj_count);
ZCACHE_SYSFS_RO_ATOMIC(curr_objnode_count);
ZCACHE_SYSFS_RO_CUSTOM(zbud_unbuddied_list_counts,
                        zbud_show_unbuddied_list_counts);
ZCACHE_SYSFS_RO_CUSTOM(zbud_cumul_chunk_counts,
                        zbud_show_cumul_chunk_counts);

static struct attribute *zcache_attrs[] = {
        &zcache_curr_obj_count_attr.attr,
        &zcache_curr_obj_count_max_attr.attr,
        &zcache_curr_objnode_count_attr.attr,
        &zcache_curr_objnode_count_max_attr.attr,
        &zcache_flush_total_attr.attr,
        &zcache_flobj_total_attr.attr,
        &zcache_flush_found_attr.attr,
        &zcache_flobj_found_attr.attr,
        &zcache_failed_eph_puts_attr.attr,
        &zcache_failed_pers_puts_attr.attr,
        &zcache_compress_poor_attr.attr,
        &zcache_zbud_curr_raw_pages_attr.attr,
        &zcache_zbud_curr_zpages_attr.attr,
        &zcache_zbud_curr_zbytes_attr.attr,
        &zcache_zbud_cumul_zpages_attr.attr,
        &zcache_zbud_cumul_zbytes_attr.attr,
        &zcache_zbud_buddied_count_attr.attr,
        &zcache_zbpg_unused_list_count_attr.attr,
        &zcache_evicted_raw_pages_attr.attr,
        &zcache_evicted_unbuddied_pages_attr.attr,
        &zcache_evicted_buddied_pages_attr.attr,
        &zcache_failed_get_free_pages_attr.attr,
        &zcache_failed_alloc_attr.attr,
        &zcache_put_to_flush_attr.attr,
        &zcache_aborted_preload_attr.attr,
        &zcache_aborted_shrink_attr.attr,
        &zcache_zbud_unbuddied_list_counts_attr.attr,
        &zcache_zbud_cumul_chunk_counts_attr.attr,
        NULL,
};

static struct attribute_group zcache_attr_group = {
        .attrs = zcache_attrs,
        .name = "zcache",
};

#endif /* CONFIG_SYSFS */
/*
 * When zcache is disabled ("frozen"), pools can be created and destroyed,
 * but all puts (and thus all other operations that require memory allocation)
 * must fail.  If zcache is unfrozen, accepts puts, then frozen again,
 * data consistency requires all puts while frozen to be converted into
 * flushes.
 */
static bool zcache_freeze;

/*
 * zcache shrinker interface (only useful for ephemeral pages, so zbud only)
 */
static int shrink_zcache_memory(struct shrinker *shrink,
                                struct shrink_control *sc)
{
        int ret = -1;
        int nr = sc->nr_to_scan;
        gfp_t gfp_mask = sc->gfp_mask;

        if (nr >= 0) {
                if (!(gfp_mask & __GFP_FS))
                        /* does this case really need to be skipped? */
                        goto out;
                if (spin_trylock(&zcache_direct_reclaim_lock)) {
                        zbud_evict_pages(nr);
                        spin_unlock(&zcache_direct_reclaim_lock);
                } else
                        zcache_aborted_shrink++;
        }
        ret = (int)atomic_read(&zcache_zbud_curr_raw_pages);
out:
        return ret;
}

static struct shrinker zcache_shrinker = {
        .shrink = shrink_zcache_memory,
        .seeks = DEFAULT_SEEKS,
};

/*
 * zcache shims between cleancache/frontswap ops and tmem
 */

static int zcache_put_page(int pool_id, struct tmem_oid *oidp,
                                uint32_t index, struct page *page)
{
        struct tmem_pool *pool;
        int ret = -1;

        BUG_ON(!irqs_disabled());
        pool = zcache_get_pool_by_id(pool_id);
        if (unlikely(pool == NULL))
                goto out;
        if (!zcache_freeze && zcache_do_preload(pool) == 0) {
                /* preload does preempt_disable on success */
                ret = tmem_put(pool, oidp, index, page);
                if (ret < 0) {
                        if (is_ephemeral(pool))
                                zcache_failed_eph_puts++;
                        else
                                zcache_failed_pers_puts++;
                }
                zcache_put_pool(pool);
                preempt_enable_no_resched();
        } else {
                zcache_put_to_flush++;
                if (atomic_read(&pool->obj_count) > 0)
                        /* the put fails whether the flush succeeds or not */
                        (void)tmem_flush_page(pool, oidp, index);
                zcache_put_pool(pool);
        }
out:
        return ret;
}

static int zcache_get_page(int pool_id, struct tmem_oid *oidp,
                                uint32_t index, struct page *page)
{
        struct tmem_pool *pool;
        int ret = -1;
        unsigned long flags;

        local_irq_save(flags);
        pool = zcache_get_pool_by_id(pool_id);
        if (likely(pool != NULL)) {
                if (atomic_read(&pool->obj_count) > 0)
                        ret = tmem_get(pool, oidp, index, page);
                zcache_put_pool(pool);
        }
        local_irq_restore(flags);
        return ret;
}

static int zcache_flush_page(int pool_id, struct tmem_oid *oidp, uint32_t index)
{
        struct tmem_pool *pool;
        int ret = -1;
        unsigned long flags;

        local_irq_save(flags);
        zcache_flush_total++;
        pool = zcache_get_pool_by_id(pool_id);
        if (likely(pool != NULL)) {
                if (atomic_read(&pool->obj_count) > 0)
                        ret = tmem_flush_page(pool, oidp, index);
                zcache_put_pool(pool);
        }
        if (ret >= 0)
                zcache_flush_found++;
        local_irq_restore(flags);
        return ret;
}

static int zcache_flush_object(int pool_id, struct tmem_oid *oidp)
{
        struct tmem_pool *pool;
        int ret = -1;
        unsigned long flags;

        local_irq_save(flags);
        zcache_flobj_total++;
        pool = zcache_get_pool_by_id(pool_id);
        if (likely(pool != NULL)) {
                if (atomic_read(&pool->obj_count) > 0)
                        ret = tmem_flush_object(pool, oidp);
                zcache_put_pool(pool);
        }
        if (ret >= 0)
                zcache_flobj_found++;
        local_irq_restore(flags);
        return ret;
}

static int zcache_destroy_pool(int pool_id)
{
        struct tmem_pool *pool = NULL;
        int ret = -1;

        if (pool_id < 0)
                goto out;
        pool = zcache_client.tmem_pools[pool_id];
        if (pool == NULL)
                goto out;
        zcache_client.tmem_pools[pool_id] = NULL;
        /* wait for pool activity on other cpus to quiesce */
        while (atomic_read(&pool->refcount) != 0)
                ;
        local_bh_disable();
        ret = tmem_destroy_pool(pool);
        local_bh_enable();
        kfree(pool);
        pr_info("zcache: destroyed pool id=%d\n", pool_id);
out:
        return ret;
}

static int zcache_new_pool(uint32_t flags)
{
        int poolid = -1;
        struct tmem_pool *pool;

        pool = kmalloc(sizeof(struct tmem_pool), GFP_KERNEL);
        if (pool == NULL) {
                pr_info("zcache: pool creation failed: out of memory\n");
                goto out;
        }

        for (poolid = 0; poolid < MAX_POOLS_PER_CLIENT; poolid++)
                if (zcache_client.tmem_pools[poolid] == NULL)
                        break;
        if (poolid >= MAX_POOLS_PER_CLIENT) {
                pr_info("zcache: pool creation failed: max exceeded\n");
                kfree(pool);
                poolid = -1;
                goto out;
        }
        atomic_set(&pool->refcount, 0);
        pool->client = &zcache_client;
        pool->pool_id = poolid;
        tmem_new_pool(pool, flags);
        zcache_client.tmem_pools[poolid] = pool;
        pr_info("zcache: created %s tmem pool, id=%d\n",
                flags & TMEM_POOL_PERSIST ? "persistent" : "ephemeral",
                poolid);
out:
        return poolid;
}

/**********
 * Two kernel functionalities currently can be layered on top of tmem.
 * These are "cleancache" which is used as a second-chance cache for clean
 * page cache pages; and "frontswap" which is used for swap pages
 * to avoid writes to disk.  A generic "shim" is provided here for each
 * to translate in-kernel semantics to zcache semantics.
 */

#ifdef CONFIG_CLEANCACHE
static void zcache_cleancache_put_page(int pool_id,
                                        struct cleancache_filekey key,
                                        pgoff_t index, struct page *page)
{
        u32 ind = (u32) index;
        struct tmem_oid oid = *(struct tmem_oid *)&key;

        if (likely(ind == index))
                (void)zcache_put_page(pool_id, &oid, index, page);
}

static int zcache_cleancache_get_page(int pool_id,
                                        struct cleancache_filekey key,
                                        pgoff_t index, struct page *page)
{
        u32 ind = (u32) index;
        struct tmem_oid oid = *(struct tmem_oid *)&key;
        int ret = -1;

        if (likely(ind == index))
                ret = zcache_get_page(pool_id, &oid, index, page);
        return ret;
}

static void zcache_cleancache_flush_page(int pool_id,
                                        struct cleancache_filekey key,
                                        pgoff_t index)
{
        u32 ind = (u32) index;
        struct tmem_oid oid = *(struct tmem_oid *)&key;

        if (likely(ind == index))
                (void)zcache_flush_page(pool_id, &oid, ind);
}

static void zcache_cleancache_flush_inode(int pool_id,
                                        struct cleancache_filekey key)
{
        struct tmem_oid oid = *(struct tmem_oid *)&key;

        (void)zcache_flush_object(pool_id, &oid);
}

static void zcache_cleancache_flush_fs(int pool_id)
{
        if (pool_id >= 0)
                (void)zcache_destroy_pool(pool_id);
}

static int zcache_cleancache_init_fs(size_t pagesize)
{
        BUG_ON(sizeof(struct cleancache_filekey) !=
                                sizeof(struct tmem_oid));
        BUG_ON(pagesize != PAGE_SIZE);
        return zcache_new_pool(0);
}

static int zcache_cleancache_init_shared_fs(char *uuid, size_t pagesize)
{
        /* shared pools are unsupported and map to private */
        BUG_ON(sizeof(struct cleancache_filekey) !=
                                sizeof(struct tmem_oid));
        BUG_ON(pagesize != PAGE_SIZE);
        return zcache_new_pool(0);
}

static struct cleancache_ops zcache_cleancache_ops = {
        .put_page = zcache_cleancache_put_page,
        .get_page = zcache_cleancache_get_page,
        .flush_page = zcache_cleancache_flush_page,
        .flush_inode = zcache_cleancache_flush_inode,
        .flush_fs = zcache_cleancache_flush_fs,
        .init_shared_fs = zcache_cleancache_init_shared_fs,
        .init_fs = zcache_cleancache_init_fs
};

struct cleancache_ops zcache_cleancache_register_ops(void)
{
        struct cleancache_ops old_ops =
                cleancache_register_ops(&zcache_cleancache_ops);

        return old_ops;
}
#endif

#ifdef CONFIG_FRONTSWAP
/* a single tmem poolid is used for all frontswap "types" (swapfiles) */
static int zcache_frontswap_poolid = -1;

/*
 * Swizzling increases objects per swaptype, increasing tmem concurrency
 * for heavy swaploads.  Later, larger nr_cpus -> larger SWIZ_BITS
 */
#define SWIZ_BITS               4
#define SWIZ_MASK               ((1 << SWIZ_BITS) - 1)
#define _oswiz(_type, _ind)     ((_type << SWIZ_BITS) | (_ind & SWIZ_MASK))
#define iswiz(_ind)             (_ind >> SWIZ_BITS)

static inline struct tmem_oid oswiz(unsigned type, u32 ind)
{
        struct tmem_oid oid = { .oid = { 0 } };
        oid.oid[0] = _oswiz(type, ind);
        return oid;
}

static int zcache_frontswap_put_page(unsigned type, pgoff_t offset,
                                   struct page *page)
{
        u64 ind64 = (u64)offset;
        u32 ind = (u32)offset;
        struct tmem_oid oid = oswiz(type, ind);
        int ret = -1;
        unsigned long flags;

        BUG_ON(!PageLocked(page));
        if (likely(ind64 == ind)) {
                local_irq_save(flags);
                ret = zcache_put_page(zcache_frontswap_poolid, &oid,
                                        iswiz(ind), page);
                local_irq_restore(flags);
        }
        return ret;
}

/* returns 0 if the page was successfully gotten from frontswap, -1 if
 * was not present (should never happen!) */
static int zcache_frontswap_get_page(unsigned type, pgoff_t offset,
                                   struct page *page)
{
        u64 ind64 = (u64)offset;
        u32 ind = (u32)offset;
        struct tmem_oid oid = oswiz(type, ind);
        int ret = -1;

        BUG_ON(!PageLocked(page));
        if (likely(ind64 == ind))
                ret = zcache_get_page(zcache_frontswap_poolid, &oid,
                                        iswiz(ind), page);
        return ret;
}

/* flush a single page from frontswap */
static void zcache_frontswap_flush_page(unsigned type, pgoff_t offset)
{
        u64 ind64 = (u64)offset;
        u32 ind = (u32)offset;
        struct tmem_oid oid = oswiz(type, ind);

        if (likely(ind64 == ind))
                (void)zcache_flush_page(zcache_frontswap_poolid, &oid,
                                        iswiz(ind));
}

/* flush all pages from the passed swaptype */
static void zcache_frontswap_flush_area(unsigned type)
{
        struct tmem_oid oid;
        int ind;

        for (ind = SWIZ_MASK; ind >= 0; ind--) {
                oid = oswiz(type, ind);
                (void)zcache_flush_object(zcache_frontswap_poolid, &oid);
        }
}

static void zcache_frontswap_init(unsigned ignored)
{
        /* a single tmem poolid is used for all frontswap "types" (swapfiles) */
        if (zcache_frontswap_poolid < 0)
                zcache_frontswap_poolid = zcache_new_pool(TMEM_POOL_PERSIST);
}

static struct frontswap_ops zcache_frontswap_ops = {
        .put_page = zcache_frontswap_put_page,
        .get_page = zcache_frontswap_get_page,
        .flush_page = zcache_frontswap_flush_page,
        .flush_area = zcache_frontswap_flush_area,
        .init = zcache_frontswap_init
};

struct frontswap_ops zcache_frontswap_register_ops(void)
{
        struct frontswap_ops old_ops =
                frontswap_register_ops(&zcache_frontswap_ops);

        return old_ops;
}
#endif

/*
 * zcache initialization
 * NOTE FOR NOW zcache MUST BE PROVIDED AS A KERNEL BOOT PARAMETER OR
 * NOTHING HAPPENS!
 */

static int zcache_enabled;

static int __init enable_zcache(char *s)
{
        zcache_enabled = 1;
        return 1;
}
__setup("zcache", enable_zcache);

/* allow independent dynamic disabling of cleancache and frontswap */

static int use_cleancache = 1;

static int __init no_cleancache(char *s)
{
        use_cleancache = 0;
        return 1;
}

__setup("nocleancache", no_cleancache);

static int use_frontswap = 1;

static int __init no_frontswap(char *s)
{
        use_frontswap = 0;
        return 1;
}

__setup("nofrontswap", no_frontswap);

static int __init zcache_init(void)
{
#ifdef CONFIG_SYSFS
        int ret = 0;

        ret = sysfs_create_group(mm_kobj, &zcache_attr_group);
        if (ret) {
                pr_err("zcache: can't create sysfs\n");
                goto out;
        }
#endif /* CONFIG_SYSFS */
#if defined(CONFIG_CLEANCACHE) || defined(CONFIG_FRONTSWAP)
        if (zcache_enabled) {
                unsigned int cpu;

                tmem_register_hostops(&zcache_hostops);
                tmem_register_pamops(&zcache_pamops);
                ret = register_cpu_notifier(&zcache_cpu_notifier_block);
                if (ret) {
                        pr_err("zcache: can't register cpu notifier\n");
                        goto out;
                }
                for_each_online_cpu(cpu) {
                        void *pcpu = (void *)(long)cpu;
                        zcache_cpu_notifier(&zcache_cpu_notifier_block,
                                CPU_UP_PREPARE, pcpu);
                }
        }
        zcache_objnode_cache = kmem_cache_create("zcache_objnode",
                                sizeof(struct tmem_objnode), 0, 0, NULL);
        zcache_obj_cache = kmem_cache_create("zcache_obj",
                                sizeof(struct tmem_obj), 0, 0, NULL);
#endif
#ifdef CONFIG_CLEANCACHE
        if (zcache_enabled && use_cleancache) {
                struct cleancache_ops old_ops;

                zbud_init();
                register_shrinker(&zcache_shrinker);
                old_ops = zcache_cleancache_register_ops();
                pr_info("zcache: cleancache enabled using kernel "
                        "transcendent memory and compression buddies\n");
                if (old_ops.init_fs != NULL)
                        pr_warning("zcache: cleancache_ops overridden");
        }
#endif
#ifdef CONFIG_FRONTSWAP
        if (zcache_enabled && use_frontswap) {
                struct frontswap_ops old_ops;

                zcache_client.xvpool = xv_create_pool();
                if (zcache_client.xvpool == NULL) {
                        pr_err("zcache: can't create xvpool\n");
                        goto out;
                }
                old_ops = zcache_frontswap_register_ops();
                pr_info("zcache: frontswap enabled using kernel "
                        "transcendent memory and xvmalloc\n");
                if (old_ops.init != NULL)
                        pr_warning("ktmem: frontswap_ops overridden");
        }
#endif
out:
        return ret;
}

module_init(zcache_init)