// SPDX-License-Identifier: GPL-2.0-only
/*
 *  linux/mm/swap.c
 *
 *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
 */

/*
 * This file contains the default values for the operation of the
 * Linux VM subsystem. Fine-tuning documentation can be found in
 * Documentation/admin-guide/sysctl/vm.rst.
 * Started 18.12.91
 * Swap aging added 23.2.95, Stephen Tweedie.
 * Buffermem limits added 12.3.98, Rik van Riel.
 */

#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/kernel_stat.h>
#include <linux/swap.h>
#include <linux/mman.h>
#include <linux/pagemap.h>
#include <linux/pagevec.h>
#include <linux/init.h>
#include <linux/export.h>
#include <linux/mm_inline.h>
#include <linux/percpu_counter.h>
#include <linux/memremap.h>
#include <linux/percpu.h>
#include <linux/cpu.h>
#include <linux/notifier.h>
#include <linux/backing-dev.h>
#include <linux/memcontrol.h>
#include <linux/gfp.h>
#include <linux/uio.h>
#include <linux/hugetlb.h>
#include <linux/page_idle.h>
#include <linux/local_lock.h>
#include <linux/buffer_head.h>

#include "internal.h"

#define CREATE_TRACE_POINTS
#include <trace/events/pagemap.h>

/* How many pages do we try to swap or page in/out together? */
int page_cluster;

/* Protecting only lru_rotate.pvec which requires disabling interrupts */
struct lru_rotate {
        local_lock_t lock;
        struct pagevec pvec;
};
static DEFINE_PER_CPU(struct lru_rotate, lru_rotate) = {
        .lock = INIT_LOCAL_LOCK(lock),
};

/*
 * The following struct pagevec are grouped together because they are protected
 * by disabling preemption (and interrupts remain enabled).
 */
struct lru_pvecs {
        local_lock_t lock;
        struct pagevec lru_add;
        struct pagevec lru_deactivate_file;
        struct pagevec lru_deactivate;
        struct pagevec lru_lazyfree;
#ifdef CONFIG_SMP
        struct pagevec activate_page;
#endif
};
static DEFINE_PER_CPU(struct lru_pvecs, lru_pvecs) = {
        .lock = INIT_LOCAL_LOCK(lock),
};

/*
 * This path almost never happens for VM activity - pages are normally
 * freed via pagevecs.  But it gets used by networking.
 */
static void __page_cache_release(struct page *page)
{
        if (PageLRU(page)) {
                struct lruvec *lruvec;
                unsigned long flags;

                lruvec = lock_page_lruvec_irqsave(page, &flags);
                del_page_from_lru_list(page, lruvec);
                __clear_page_lru_flags(page);
                unlock_page_lruvec_irqrestore(lruvec, flags);
        }
        __ClearPageWaiters(page);
}

static void __put_single_page(struct page *page)
{
        __page_cache_release(page);
        mem_cgroup_uncharge(page);
        free_unref_page(page, 0);
}

static void __put_compound_page(struct page *page)
{
        /*
         * __page_cache_release() is supposed to be called for thp, not for
         * hugetlb. This is because hugetlb page does never have PageLRU set
         * (it's never listed to any LRU lists) and no memcg routines should
         * be called for hugetlb (it has a separate hugetlb_cgroup.)
         */
        if (!PageHuge(page))
                __page_cache_release(page);
        destroy_compound_page(page);
}

void __put_page(struct page *page)
{
        if (is_zone_device_page(page)) {
                put_dev_pagemap(page->pgmap);

                /*
                 * The page belongs to the device that created pgmap. Do
                 * not return it to page allocator.
                 */
                return;
        }

        if (unlikely(PageCompound(page)))
                __put_compound_page(page);
        else
                __put_single_page(page);
}
EXPORT_SYMBOL(__put_page);

/**
 * put_pages_list() - release a list of pages
 * @pages: list of pages threaded on page->lru
 *
 * Release a list of pages which are strung together on page.lru.  Currently
 * used by read_cache_pages() and related error recovery code.
 */
void put_pages_list(struct list_head *pages)
{
        while (!list_empty(pages)) {
                struct page *victim;

                victim = lru_to_page(pages);
                list_del(&victim->lru);
                put_page(victim);
        }
}
EXPORT_SYMBOL(put_pages_list);

/*
 * get_kernel_pages() - pin kernel pages in memory
 * @kiov:       An array of struct kvec structures
 * @nr_segs:    number of segments to pin
 * @write:      pinning for read/write, currently ignored
 * @pages:      array that receives pointers to the pages pinned.
 *              Should be at least nr_segs long.
 *
 * Returns number of pages pinned. This may be fewer than the number
 * requested. If nr_pages is 0 or negative, returns 0. If no pages
 * were pinned, returns -errno. Each page returned must be released
 * with a put_page() call when it is finished with.
 */
int get_kernel_pages(const struct kvec *kiov, int nr_segs, int write,
                struct page **pages)
{
        int seg;

        for (seg = 0; seg < nr_segs; seg++) {
                if (WARN_ON(kiov[seg].iov_len != PAGE_SIZE))
                        return seg;

                pages[seg] = kmap_to_page(kiov[seg].iov_base);
                get_page(pages[seg]);
        }

        return seg;
}
EXPORT_SYMBOL_GPL(get_kernel_pages);

static void pagevec_lru_move_fn(struct pagevec *pvec,
        void (*move_fn)(struct page *page, struct lruvec *lruvec))
{
        int i;
        struct lruvec *lruvec = NULL;
        unsigned long flags = 0;

        for (i = 0; i < pagevec_count(pvec); i++) {
                struct page *page = pvec->pages[i];

                /* block memcg migration during page moving between lru */
                if (!TestClearPageLRU(page))
                        continue;

                lruvec = relock_page_lruvec_irqsave(page, lruvec, &flags);
                (*move_fn)(page, lruvec);

                SetPageLRU(page);
        }
        if (lruvec)
                unlock_page_lruvec_irqrestore(lruvec, flags);
        release_pages(pvec->pages, pvec->nr);
        pagevec_reinit(pvec);
}

static void pagevec_move_tail_fn(struct page *page, struct lruvec *lruvec)
{
        if (!PageUnevictable(page)) {
                del_page_from_lru_list(page, lruvec);
                ClearPageActive(page);
                add_page_to_lru_list_tail(page, lruvec);
                __count_vm_events(PGROTATED, thp_nr_pages(page));
        }
}

/* return true if pagevec needs to drain */
static bool pagevec_add_and_need_flush(struct pagevec *pvec, struct page *page)
{
        bool ret = false;

        if (!pagevec_add(pvec, page) || PageCompound(page) ||
                        lru_cache_disabled())
                ret = true;

        return ret;
}

/*
 * Writeback is about to end against a page which has been marked for immediate
 * reclaim.  If it still appears to be reclaimable, move it to the tail of the
 * inactive list.
 *
 * rotate_reclaimable_page() must disable IRQs, to prevent nasty races.
 */
void rotate_reclaimable_page(struct page *page)
{
        if (!PageLocked(page) && !PageDirty(page) &&
            !PageUnevictable(page) && PageLRU(page)) {
                struct pagevec *pvec;
                unsigned long flags;

                get_page(page);
                local_lock_irqsave(&lru_rotate.lock, flags);
                pvec = this_cpu_ptr(&lru_rotate.pvec);
                if (pagevec_add_and_need_flush(pvec, page))
                        pagevec_lru_move_fn(pvec, pagevec_move_tail_fn);
                local_unlock_irqrestore(&lru_rotate.lock, flags);
        }
}

void lru_note_cost(struct lruvec *lruvec, bool file, unsigned int nr_pages)
{
        do {
                unsigned long lrusize;

                /*
                 * Hold lruvec->lru_lock is safe here, since
                 * 1) The pinned lruvec in reclaim, or
                 * 2) From a pre-LRU page during refault (which also holds the
                 *    rcu lock, so would be safe even if the page was on the LRU
                 *    and could move simultaneously to a new lruvec).
                 */
                spin_lock_irq(&lruvec->lru_lock);
                /* Record cost event */
                if (file)
                        lruvec->file_cost += nr_pages;
                else
                        lruvec->anon_cost += nr_pages;

                /*
                 * Decay previous events
                 *
                 * Because workloads change over time (and to avoid
                 * overflow) we keep these statistics as a floating
                 * average, which ends up weighing recent refaults
                 * more than old ones.
                 */
                lrusize = lruvec_page_state(lruvec, NR_INACTIVE_ANON) +
                          lruvec_page_state(lruvec, NR_ACTIVE_ANON) +
                          lruvec_page_state(lruvec, NR_INACTIVE_FILE) +
                          lruvec_page_state(lruvec, NR_ACTIVE_FILE);

                if (lruvec->file_cost + lruvec->anon_cost > lrusize / 4) {
                        lruvec->file_cost /= 2;
                        lruvec->anon_cost /= 2;
                }
                spin_unlock_irq(&lruvec->lru_lock);
        } while ((lruvec = parent_lruvec(lruvec)));
}

void lru_note_cost_page(struct page *page)
{
        lru_note_cost(mem_cgroup_page_lruvec(page),
                      page_is_file_lru(page), thp_nr_pages(page));
}

static void __activate_page(struct page *page, struct lruvec *lruvec)
{
        if (!PageActive(page) && !PageUnevictable(page)) {
                int nr_pages = thp_nr_pages(page);

                del_page_from_lru_list(page, lruvec);
                SetPageActive(page);
                add_page_to_lru_list(page, lruvec);
                trace_mm_lru_activate(page);

                __count_vm_events(PGACTIVATE, nr_pages);
                __count_memcg_events(lruvec_memcg(lruvec), PGACTIVATE,
                                     nr_pages);
        }
}

#ifdef CONFIG_SMP
static void activate_page_drain(int cpu)
{
        struct pagevec *pvec = &per_cpu(lru_pvecs.activate_page, cpu);

        if (pagevec_count(pvec))
                pagevec_lru_move_fn(pvec, __activate_page);
}

static bool need_activate_page_drain(int cpu)
{
        return pagevec_count(&per_cpu(lru_pvecs.activate_page, cpu)) != 0;
}

static void activate_page(struct page *page)
{
        page = compound_head(page);
        if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
                struct pagevec *pvec;

                local_lock(&lru_pvecs.lock);
                pvec = this_cpu_ptr(&lru_pvecs.activate_page);
                get_page(page);
                if (pagevec_add_and_need_flush(pvec, page))
                        pagevec_lru_move_fn(pvec, __activate_page);
                local_unlock(&lru_pvecs.lock);
        }
}

#else
static inline void activate_page_drain(int cpu)
{
}

static void activate_page(struct page *page)
{
        struct lruvec *lruvec;

        page = compound_head(page);
        if (TestClearPageLRU(page)) {
                lruvec = lock_page_lruvec_irq(page);
                __activate_page(page, lruvec);
                unlock_page_lruvec_irq(lruvec);
                SetPageLRU(page);
        }
}
#endif

static void __lru_cache_activate_page(struct page *page)
{
        struct pagevec *pvec;
        int i;

        local_lock(&lru_pvecs.lock);
        pvec = this_cpu_ptr(&lru_pvecs.lru_add);

        /*
         * Search backwards on the optimistic assumption that the page being
         * activated has just been added to this pagevec. Note that only
         * the local pagevec is examined as a !PageLRU page could be in the
         * process of being released, reclaimed, migrated or on a remote
         * pagevec that is currently being drained. Furthermore, marking
         * a remote pagevec's page PageActive potentially hits a race where
         * a page is marked PageActive just after it is added to the inactive
         * list causing accounting errors and BUG_ON checks to trigger.
         */
        for (i = pagevec_count(pvec) - 1; i >= 0; i--) {
                struct page *pagevec_page = pvec->pages[i];

                if (pagevec_page == page) {
                        SetPageActive(page);
                        break;
                }
        }

        local_unlock(&lru_pvecs.lock);
}

/*
 * Mark a page as having seen activity.
 *
 * inactive,unreferenced        ->      inactive,referenced
 * inactive,referenced          ->      active,unreferenced
 * active,unreferenced          ->      active,referenced
 *
 * When a newly allocated page is not yet visible, so safe for non-atomic ops,
 * __SetPageReferenced(page) may be substituted for mark_page_accessed(page).
 */
void mark_page_accessed(struct page *page)
{
        page = compound_head(page);

        if (!PageReferenced(page)) {
                SetPageReferenced(page);
        } else if (PageUnevictable(page)) {
                /*
                 * Unevictable pages are on the "LRU_UNEVICTABLE" list. But,
                 * this list is never rotated or maintained, so marking an
                 * evictable page accessed has no effect.
                 */
        } else if (!PageActive(page)) {
                /*
                 * If the page is on the LRU, queue it for activation via
                 * lru_pvecs.activate_page. Otherwise, assume the page is on a
                 * pagevec, mark it active and it'll be moved to the active
                 * LRU on the next drain.
                 */
                if (PageLRU(page))
                        activate_page(page);
                else
                        __lru_cache_activate_page(page);
                ClearPageReferenced(page);
                workingset_activation(page);
        }
        if (page_is_idle(page))
                clear_page_idle(page);
}
EXPORT_SYMBOL(mark_page_accessed);

/**
 * lru_cache_add - add a page to a page list
 * @page: the page to be added to the LRU.
 *
 * Queue the page for addition to the LRU via pagevec. The decision on whether
 * to add the page to the [in]active [file|anon] list is deferred until the
 * pagevec is drained. This gives a chance for the caller of lru_cache_add()
 * have the page added to the active list using mark_page_accessed().
 */
void lru_cache_add(struct page *page)
{
        struct pagevec *pvec;

        VM_BUG_ON_PAGE(PageActive(page) && PageUnevictable(page), page);
        VM_BUG_ON_PAGE(PageLRU(page), page);

        get_page(page);
        local_lock(&lru_pvecs.lock);
        pvec = this_cpu_ptr(&lru_pvecs.lru_add);
        if (pagevec_add_and_need_flush(pvec, page))
                __pagevec_lru_add(pvec);
        local_unlock(&lru_pvecs.lock);
}
EXPORT_SYMBOL(lru_cache_add);

/**
 * lru_cache_add_inactive_or_unevictable
 * @page:  the page to be added to LRU
 * @vma:   vma in which page is mapped for determining reclaimability
 *
 * Place @page on the inactive or unevictable LRU list, depending on its
 * evictability.
 */
void lru_cache_add_inactive_or_unevictable(struct page *page,
                                         struct vm_area_struct *vma)
{
        bool unevictable;

        VM_BUG_ON_PAGE(PageLRU(page), page);

        unevictable = (vma->vm_flags & (VM_LOCKED | VM_SPECIAL)) == VM_LOCKED;
        if (unlikely(unevictable) && !TestSetPageMlocked(page)) {
                int nr_pages = thp_nr_pages(page);
                /*
                 * We use the irq-unsafe __mod_zone_page_state because this
                 * counter is not modified from interrupt context, and the pte
                 * lock is held(spinlock), which implies preemption disabled.
                 */
                __mod_zone_page_state(page_zone(page), NR_MLOCK, nr_pages);
                count_vm_events(UNEVICTABLE_PGMLOCKED, nr_pages);
        }
        lru_cache_add(page);
}

/*
 * If the page can not be invalidated, it is moved to the
 * inactive list to speed up its reclaim.  It is moved to the
 * head of the list, rather than the tail, to give the flusher
 * threads some time to write it out, as this is much more
 * effective than the single-page writeout from reclaim.
 *
 * If the page isn't page_mapped and dirty/writeback, the page
 * could reclaim asap using PG_reclaim.
 *
 * 1. active, mapped page -> none
 * 2. active, dirty/writeback page -> inactive, head, PG_reclaim
 * 3. inactive, mapped page -> none
 * 4. inactive, dirty/writeback page -> inactive, head, PG_reclaim
 * 5. inactive, clean -> inactive, tail
 * 6. Others -> none
 *
 * In 4, why it moves inactive's head, the VM expects the page would
 * be write it out by flusher threads as this is much more effective
 * than the single-page writeout from reclaim.
 */
static void lru_deactivate_file_fn(struct page *page, struct lruvec *lruvec)
{
        bool active = PageActive(page);
        int nr_pages = thp_nr_pages(page);

        if (PageUnevictable(page))
                return;

        /* Some processes are using the page */
        if (page_mapped(page))
                return;

        del_page_from_lru_list(page, lruvec);
        ClearPageActive(page);
        ClearPageReferenced(page);

        if (PageWriteback(page) || PageDirty(page)) {
                /*
                 * PG_reclaim could be raced with end_page_writeback
                 * It can make readahead confusing.  But race window
                 * is _really_ small and  it's non-critical problem.
                 */
                add_page_to_lru_list(page, lruvec);
                SetPageReclaim(page);
        } else {
                /*
                 * The page's writeback ends up during pagevec
                 * We move that page into tail of inactive.
                 */
                add_page_to_lru_list_tail(page, lruvec);
                __count_vm_events(PGROTATED, nr_pages);
        }

        if (active) {
                __count_vm_events(PGDEACTIVATE, nr_pages);
                __count_memcg_events(lruvec_memcg(lruvec), PGDEACTIVATE,
                                     nr_pages);
        }
}

static void lru_deactivate_fn(struct page *page, struct lruvec *lruvec)
{
        if (PageActive(page) && !PageUnevictable(page)) {
                int nr_pages = thp_nr_pages(page);

                del_page_from_lru_list(page, lruvec);
                ClearPageActive(page);
                ClearPageReferenced(page);
                add_page_to_lru_list(page, lruvec);

                __count_vm_events(PGDEACTIVATE, nr_pages);
                __count_memcg_events(lruvec_memcg(lruvec), PGDEACTIVATE,
                                     nr_pages);
        }
}

static void lru_lazyfree_fn(struct page *page, struct lruvec *lruvec)
{
        if (PageAnon(page) && PageSwapBacked(page) &&
            !PageSwapCache(page) && !PageUnevictable(page)) {
                int nr_pages = thp_nr_pages(page);

                del_page_from_lru_list(page, lruvec);
                ClearPageActive(page);
                ClearPageReferenced(page);
                /*
                 * Lazyfree pages are clean anonymous pages.  They have
                 * PG_swapbacked flag cleared, to distinguish them from normal
                 * anonymous pages
                 */
                ClearPageSwapBacked(page);
                add_page_to_lru_list(page, lruvec);

                __count_vm_events(PGLAZYFREE, nr_pages);
                __count_memcg_events(lruvec_memcg(lruvec), PGLAZYFREE,
                                     nr_pages);
        }
}

/*
 * Drain pages out of the cpu's pagevecs.
 * Either "cpu" is the current CPU, and preemption has already been
 * disabled; or "cpu" is being hot-unplugged, and is already dead.
 */
void lru_add_drain_cpu(int cpu)
{
        struct pagevec *pvec = &per_cpu(lru_pvecs.lru_add, cpu);

        if (pagevec_count(pvec))
                __pagevec_lru_add(pvec);

        pvec = &per_cpu(lru_rotate.pvec, cpu);
        /* Disabling interrupts below acts as a compiler barrier. */
        if (data_race(pagevec_count(pvec))) {
                unsigned long flags;

                /* No harm done if a racing interrupt already did this */
                local_lock_irqsave(&lru_rotate.lock, flags);
                pagevec_lru_move_fn(pvec, pagevec_move_tail_fn);
                local_unlock_irqrestore(&lru_rotate.lock, flags);
        }

        pvec = &per_cpu(lru_pvecs.lru_deactivate_file, cpu);
        if (pagevec_count(pvec))
                pagevec_lru_move_fn(pvec, lru_deactivate_file_fn);

        pvec = &per_cpu(lru_pvecs.lru_deactivate, cpu);
        if (pagevec_count(pvec))
                pagevec_lru_move_fn(pvec, lru_deactivate_fn);

        pvec = &per_cpu(lru_pvecs.lru_lazyfree, cpu);
        if (pagevec_count(pvec))
                pagevec_lru_move_fn(pvec, lru_lazyfree_fn);

        activate_page_drain(cpu);
}

/**
 * deactivate_file_page - forcefully deactivate a file page
 * @page: page to deactivate
 *
 * This function hints the VM that @page is a good reclaim candidate,
 * for example if its invalidation fails due to the page being dirty
 * or under writeback.
 */
void deactivate_file_page(struct page *page)
{
        /*
         * In a workload with many unevictable page such as mprotect,
         * unevictable page deactivation for accelerating reclaim is pointless.
         */
        if (PageUnevictable(page))
                return;

        if (likely(get_page_unless_zero(page))) {
                struct pagevec *pvec;

                local_lock(&lru_pvecs.lock);
                pvec = this_cpu_ptr(&lru_pvecs.lru_deactivate_file);

                if (pagevec_add_and_need_flush(pvec, page))
                        pagevec_lru_move_fn(pvec, lru_deactivate_file_fn);
                local_unlock(&lru_pvecs.lock);
        }
}

/*
 * deactivate_page - deactivate a page
 * @page: page to deactivate
 *
 * deactivate_page() moves @page to the inactive list if @page was on the active
 * list and was not an unevictable page.  This is done to accelerate the reclaim
 * of @page.
 */
void deactivate_page(struct page *page)
{
        if (PageLRU(page) && PageActive(page) && !PageUnevictable(page)) {
                struct pagevec *pvec;

                local_lock(&lru_pvecs.lock);
                pvec = this_cpu_ptr(&lru_pvecs.lru_deactivate);
                get_page(page);
                if (pagevec_add_and_need_flush(pvec, page))
                        pagevec_lru_move_fn(pvec, lru_deactivate_fn);
                local_unlock(&lru_pvecs.lock);
        }
}

/**
 * mark_page_lazyfree - make an anon page lazyfree
 * @page: page to deactivate
 *
 * mark_page_lazyfree() moves @page to the inactive file list.
 * This is done to accelerate the reclaim of @page.
 */
void mark_page_lazyfree(struct page *page)
{
        if (PageLRU(page) && PageAnon(page) && PageSwapBacked(page) &&
            !PageSwapCache(page) && !PageUnevictable(page)) {
                struct pagevec *pvec;

                local_lock(&lru_pvecs.lock);
                pvec = this_cpu_ptr(&lru_pvecs.lru_lazyfree);
                get_page(page);
                if (pagevec_add_and_need_flush(pvec, page))
                        pagevec_lru_move_fn(pvec, lru_lazyfree_fn);
                local_unlock(&lru_pvecs.lock);
        }
}

void lru_add_drain(void)
{
        local_lock(&lru_pvecs.lock);
        lru_add_drain_cpu(smp_processor_id());
        local_unlock(&lru_pvecs.lock);
}

/*
 * It's called from per-cpu workqueue context in SMP case so
 * lru_add_drain_cpu and invalidate_bh_lrus_cpu should run on
 * the same cpu. It shouldn't be a problem in !SMP case since
 * the core is only one and the locks will disable preemption.
 */
static void lru_add_and_bh_lrus_drain(void)
{
        local_lock(&lru_pvecs.lock);
        lru_add_drain_cpu(smp_processor_id());
        local_unlock(&lru_pvecs.lock);
        invalidate_bh_lrus_cpu();
}

void lru_add_drain_cpu_zone(struct zone *zone)
{
        local_lock(&lru_pvecs.lock);
        lru_add_drain_cpu(smp_processor_id());
        drain_local_pages(zone);
        local_unlock(&lru_pvecs.lock);
}

#ifdef CONFIG_SMP

static DEFINE_PER_CPU(struct work_struct, lru_add_drain_work);

static void lru_add_drain_per_cpu(struct work_struct *dummy)
{
        lru_add_and_bh_lrus_drain();
}

/*
 * Doesn't need any cpu hotplug locking because we do rely on per-cpu
 * kworkers being shut down before our page_alloc_cpu_dead callback is
 * executed on the offlined cpu.
 * Calling this function with cpu hotplug locks held can actually lead
 * to obscure indirect dependencies via WQ context.
 */
inline void __lru_add_drain_all(bool force_all_cpus)
{
        /*
         * lru_drain_gen - Global pages generation number
         *
         * (A) Definition: global lru_drain_gen = x implies that all generations
         *     0 < n <= x are already *scheduled* for draining.
         *
         * This is an optimization for the highly-contended use case where a
         * user space workload keeps constantly generating a flow of pages for
         * each CPU.
         */
        static unsigned int lru_drain_gen;
        static struct cpumask has_work;
        static DEFINE_MUTEX(lock);
        unsigned cpu, this_gen;

        /*
         * Make sure nobody triggers this path before mm_percpu_wq is fully
         * initialized.
         */
        if (WARN_ON(!mm_percpu_wq))
                return;

        /*
         * Guarantee pagevec counter stores visible by this CPU are visible to
         * other CPUs before loading the current drain generation.
         */
        smp_mb();

        /*
         * (B) Locally cache global LRU draining generation number
         *
         * The read barrier ensures that the counter is loaded before the mutex
         * is taken. It pairs with smp_mb() inside the mutex critical section
         * at (D).
         */
        this_gen = smp_load_acquire(&lru_drain_gen);

        mutex_lock(&lock);

        /*
         * (C) Exit the draining operation if a newer generation, from another
         * lru_add_drain_all(), was already scheduled for draining. Check (A).
         */
        if (unlikely(this_gen != lru_drain_gen && !force_all_cpus))
                goto done;

        /*
         * (D) Increment global generation number
         *
         * Pairs with smp_load_acquire() at (B), outside of the critical
         * section. Use a full memory barrier to guarantee that the new global
         * drain generation number is stored before loading pagevec counters.
         *
         * This pairing must be done here, before the for_each_online_cpu loop
         * below which drains the page vectors.
         *
         * Let x, y, and z represent some system CPU numbers, where x < y < z.
         * Assume CPU #z is in the middle of the for_each_online_cpu loop
         * below and has already reached CPU #y's per-cpu data. CPU #x comes
         * along, adds some pages to its per-cpu vectors, then calls
         * lru_add_drain_all().
         *
         * If the paired barrier is done at any later step, e.g. after the
         * loop, CPU #x will just exit at (C) and miss flushing out all of its
         * added pages.
         */
        WRITE_ONCE(lru_drain_gen, lru_drain_gen + 1);
        smp_mb();

        cpumask_clear(&has_work);
        for_each_online_cpu(cpu) {
                struct work_struct *work = &per_cpu(lru_add_drain_work, cpu);

                if (force_all_cpus ||
                    pagevec_count(&per_cpu(lru_pvecs.lru_add, cpu)) ||
                    data_race(pagevec_count(&per_cpu(lru_rotate.pvec, cpu))) ||
                    pagevec_count(&per_cpu(lru_pvecs.lru_deactivate_file, cpu)) ||
                    pagevec_count(&per_cpu(lru_pvecs.lru_deactivate, cpu)) ||
                    pagevec_count(&per_cpu(lru_pvecs.lru_lazyfree, cpu)) ||
                    need_activate_page_drain(cpu) ||
                    has_bh_in_lru(cpu, NULL)) {
                        INIT_WORK(work, lru_add_drain_per_cpu);
                        queue_work_on(cpu, mm_percpu_wq, work);
                        __cpumask_set_cpu(cpu, &has_work);
                }
        }

        for_each_cpu(cpu, &has_work)
                flush_work(&per_cpu(lru_add_drain_work, cpu));

done:
        mutex_unlock(&lock);
}

void lru_add_drain_all(void)
{
        __lru_add_drain_all(false);
}
#else
void lru_add_drain_all(void)
{
        lru_add_drain();
}
#endif /* CONFIG_SMP */

atomic_t lru_disable_count = ATOMIC_INIT(0);

/*
 * lru_cache_disable() needs to be called before we start compiling
 * a list of pages to be migrated using isolate_lru_page().
 * It drains pages on LRU cache and then disable on all cpus until
 * lru_cache_enable is called.
 *
 * Must be paired with a call to lru_cache_enable().
 */
void lru_cache_disable(void)
{
        atomic_inc(&lru_disable_count);
#ifdef CONFIG_SMP
        /*
         * lru_add_drain_all in the force mode will schedule draining on
         * all online CPUs so any calls of lru_cache_disabled wrapped by
         * local_lock or preemption disabled would be ordered by that.
         * The atomic operation doesn't need to have stronger ordering
         * requirements because that is enforeced by the scheduling
         * guarantees.
         */
        __lru_add_drain_all(true);
#else
        lru_add_and_bh_lrus_drain();
#endif
}

/**
 * release_pages - batched put_page()
 * @pages: array of pages to release
 * @nr: number of pages
 *
 * Decrement the reference count on all the pages in @pages.  If it
 * fell to zero, remove the page from the LRU and free it.
 */
void release_pages(struct page **pages, int nr)
{
        int i;
        LIST_HEAD(pages_to_free);
        struct lruvec *lruvec = NULL;
        unsigned long flags;
        unsigned int lock_batch;

        for (i = 0; i < nr; i++) {
                struct page *page = pages[i];

                /*
                 * Make sure the IRQ-safe lock-holding time does not get
                 * excessive with a continuous string of pages from the
                 * same lruvec. The lock is held only if lruvec != NULL.
                 */
                if (lruvec && ++lock_batch == SWAP_CLUSTER_MAX) {
                        unlock_page_lruvec_irqrestore(lruvec, flags);
                        lruvec = NULL;
                }

                page = compound_head(page);
                if (is_huge_zero_page(page))
                        continue;

                if (is_zone_device_page(page)) {
                        if (lruvec) {
                                unlock_page_lruvec_irqrestore(lruvec, flags);
                                lruvec = NULL;
                        }
                        /*
                         * ZONE_DEVICE pages that return 'false' from
                         * page_is_devmap_managed() do not require special
                         * processing, and instead, expect a call to
                         * put_page_testzero().
                         */
                        if (page_is_devmap_managed(page)) {
                                put_devmap_managed_page(page);
                                continue;
                        }
                        if (put_page_testzero(page))
                                put_dev_pagemap(page->pgmap);
                        continue;
                }

                if (!put_page_testzero(page))
                        continue;

                if (PageCompound(page)) {
                        if (lruvec) {
                                unlock_page_lruvec_irqrestore(lruvec, flags);
                                lruvec = NULL;
                        }
                        __put_compound_page(page);
                        continue;
                }

                if (PageLRU(page)) {
                        struct lruvec *prev_lruvec = lruvec;

                        lruvec = relock_page_lruvec_irqsave(page, lruvec,
                                                                        &flags);
                        if (prev_lruvec != lruvec)
                                lock_batch = 0;

                        del_page_from_lru_list(page, lruvec);
                        __clear_page_lru_flags(page);
                }

                __ClearPageWaiters(page);

                list_add(&page->lru, &pages_to_free);
        }
        if (lruvec)
                unlock_page_lruvec_irqrestore(lruvec, flags);

        mem_cgroup_uncharge_list(&pages_to_free);
        free_unref_page_list(&pages_to_free);
}
EXPORT_SYMBOL(release_pages);

/*
 * The pages which we're about to release may be in the deferred lru-addition
 * queues.  That would prevent them from really being freed right now.  That's
 * OK from a correctness point of view but is inefficient - those pages may be
 * cache-warm and we want to give them back to the page allocator ASAP.
 *
 * So __pagevec_release() will drain those queues here.  __pagevec_lru_add()
 * and __pagevec_lru_add_active() call release_pages() directly to avoid
 * mutual recursion.
 */
void __pagevec_release(struct pagevec *pvec)
{
        if (!pvec->percpu_pvec_drained) {
                lru_add_drain();
                pvec->percpu_pvec_drained = true;
        }
        release_pages(pvec->pages, pagevec_count(pvec));
        pagevec_reinit(pvec);
}
EXPORT_SYMBOL(__pagevec_release);

static void __pagevec_lru_add_fn(struct page *page, struct lruvec *lruvec)
{
        int was_unevictable = TestClearPageUnevictable(page);
        int nr_pages = thp_nr_pages(page);

        VM_BUG_ON_PAGE(PageLRU(page), page);

        /*
         * Page becomes evictable in two ways:
         * 1) Within LRU lock [munlock_vma_page() and __munlock_pagevec()].
         * 2) Before acquiring LRU lock to put the page to correct LRU and then
         *   a) do PageLRU check with lock [check_move_unevictable_pages]
         *   b) do PageLRU check before lock [clear_page_mlock]

         *
         * (1) & (2a) are ok as LRU lock will serialize them. For (2b), we need
         * following strict ordering:
         *
         * #0: __pagevec_lru_add_fn             #1: clear_page_mlock
         *
         * SetPageLRU()                         TestClearPageMlocked()
         * smp_mb() // explicit ordering        // above provides strict
         *                                      // ordering
         * PageMlocked()                        PageLRU()
         *
         *
         * if '#1' does not observe setting of PG_lru by '#0' and fails
         * isolation, the explicit barrier will make sure that page_evictable
         * check will put the page in correct LRU. Without smp_mb(), SetPageLRU
         * can be reordered after PageMlocked check and can make '#1' to fail
         * the isolation of the page whose Mlocked bit is cleared (#0 is also
         * looking at the same page) and the evictable page will be stranded
         * in an unevictable LRU.
         */
        SetPageLRU(page);
        smp_mb__after_atomic();

        if (page_evictable(page)) {
                if (was_unevictable)
                        __count_vm_events(UNEVICTABLE_PGRESCUED, nr_pages);
        } else {
                ClearPageActive(page);
                SetPageUnevictable(page);
                if (!was_unevictable)
                        __count_vm_events(UNEVICTABLE_PGCULLED, nr_pages);
        }

        add_page_to_lru_list(page, lruvec);
        trace_mm_lru_insertion(page);
}

/*
 * Add the passed pages to the LRU, then drop the caller's refcount
 * on them.  Reinitialises the caller's pagevec.
 */
void __pagevec_lru_add(struct pagevec *pvec)
{
        int i;
        struct lruvec *lruvec = NULL;
        unsigned long flags = 0;

        for (i = 0; i < pagevec_count(pvec); i++) {
                struct page *page = pvec->pages[i];

                lruvec = relock_page_lruvec_irqsave(page, lruvec, &flags);
                __pagevec_lru_add_fn(page, lruvec);
        }
        if (lruvec)
                unlock_page_lruvec_irqrestore(lruvec, flags);
        release_pages(pvec->pages, pvec->nr);
        pagevec_reinit(pvec);
}

/**
 * pagevec_remove_exceptionals - pagevec exceptionals pruning
 * @pvec:       The pagevec to prune
 *
 * find_get_entries() fills both pages and XArray value entries (aka
 * exceptional entries) into the pagevec.  This function prunes all
 * exceptionals from @pvec without leaving holes, so that it can be
 * passed on to page-only pagevec operations.
 */
void pagevec_remove_exceptionals(struct pagevec *pvec)
{
        int i, j;

        for (i = 0, j = 0; i < pagevec_count(pvec); i++) {
                struct page *page = pvec->pages[i];
                if (!xa_is_value(page))
                        pvec->pages[j++] = page;
        }
        pvec->nr = j;
}

/**
 * pagevec_lookup_range - gang pagecache lookup
 * @pvec:       Where the resulting pages are placed
 * @mapping:    The address_space to search
 * @start:      The starting page index
 * @end:        The final page index
 *
 * pagevec_lookup_range() will search for & return a group of up to PAGEVEC_SIZE
 * pages in the mapping starting from index @start and upto index @end
 * (inclusive).  The pages are placed in @pvec.  pagevec_lookup() takes a
 * reference against the pages in @pvec.
 *
 * The search returns a group of mapping-contiguous pages with ascending
 * indexes.  There may be holes in the indices due to not-present pages. We
 * also update @start to index the next page for the traversal.
 *
 * pagevec_lookup_range() returns the number of pages which were found. If this
 * number is smaller than PAGEVEC_SIZE, the end of specified range has been
 * reached.
 */
unsigned pagevec_lookup_range(struct pagevec *pvec,
                struct address_space *mapping, pgoff_t *start, pgoff_t end)
{
        pvec->nr = find_get_pages_range(mapping, start, end, PAGEVEC_SIZE,
                                        pvec->pages);
        return pagevec_count(pvec);
}
EXPORT_SYMBOL(pagevec_lookup_range);

unsigned pagevec_lookup_range_tag(struct pagevec *pvec,
                struct address_space *mapping, pgoff_t *index, pgoff_t end,
                xa_mark_t tag)
{
        pvec->nr = find_get_pages_range_tag(mapping, index, end, tag,
                                        PAGEVEC_SIZE, pvec->pages);
        return pagevec_count(pvec);
}
EXPORT_SYMBOL(pagevec_lookup_range_tag);

/*
 * Perform any setup for the swap system
 */
void __init swap_setup(void)
{
        unsigned long megs = totalram_pages() >> (20 - PAGE_SHIFT);

        /* Use a smaller cluster for small-memory machines */
        if (megs < 16)
                page_cluster = 2;
        else
                page_cluster = 3;
        /*
         * Right now other parts of the system means that we
         * _really_ don't want to cluster much more
         */
}

#ifdef CONFIG_DEV_PAGEMAP_OPS
void put_devmap_managed_page(struct page *page)
{
        int count;

        if (WARN_ON_ONCE(!page_is_devmap_managed(page)))
                return;

        count = page_ref_dec_return(page);

        /*
         * devmap page refcounts are 1-based, rather than 0-based: if
         * refcount is 1, then the page is free and the refcount is
         * stable because nobody holds a reference on the page.
         */
        if (count == 1)
                free_devmap_managed_page(page);
        else if (!count)
                __put_page(page);
}
EXPORT_SYMBOL(put_devmap_managed_page);
#endif