// 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 - and for compound pages.
 */
static void __page_cache_release(struct page *page)
{
        if (PageLRU(page)) {
                struct folio *folio = page_folio(page);
                struct lruvec *lruvec;
                unsigned long flags;

                lruvec = folio_lruvec_lock_irqsave(folio, &flags);
                del_page_from_lru_list(page, lruvec);
                __clear_page_lru_flags(page);
                unlock_page_lruvec_irqrestore(lruvec, flags);
        }
        /* See comment on PageMlocked in release_pages() */
        if (unlikely(PageMlocked(page))) {
                int nr_pages = thp_nr_pages(page);

                __ClearPageMlocked(page);
                mod_zone_page_state(page_zone(page), NR_MLOCK, -nr_pages);
                count_vm_events(UNEVICTABLE_PGCLEARED, nr_pages);
        }
}

static void __put_single_page(struct page *page)
{
        __page_cache_release(page);
        mem_cgroup_uncharge(page_folio(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 (unlikely(is_zone_device_page(page)))
                free_zone_device_page(page);
        else 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.
 */
void put_pages_list(struct list_head *pages)
{
        struct page *page, *next;

        list_for_each_entry_safe(page, next, pages, lru) {
                if (!put_page_testzero(page)) {
                        list_del(&page->lru);
                        continue;
                }
                if (PageHead(page)) {
                        list_del(&page->lru);
                        __put_compound_page(page);
                        continue;
                }
                /* Cannot be PageLRU because it's passed to us using the lru */
        }

        free_unref_page_list(pages);
        INIT_LIST_HEAD(pages);
}
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_segs is 0 or negative, returns 0.  If no pages were pinned, returns 0.
 * 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];
                struct folio *folio = page_folio(page);

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

                lruvec = folio_lruvec_relock_irqsave(folio, 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)
{
        struct folio *folio = page_folio(page);

        if (!folio_test_unevictable(folio)) {
                lruvec_del_folio(lruvec, folio);
                folio_clear_active(folio);
                lruvec_add_folio_tail(lruvec, folio);
                __count_vm_events(PGROTATED, folio_nr_pages(folio));
        }
}

/* 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 folio which has been marked for
 * immediate reclaim.  If it still appears to be reclaimable, move it
 * to the tail of the inactive list.
 *
 * folio_rotate_reclaimable() must disable IRQs, to prevent nasty races.
 */
void folio_rotate_reclaimable(struct folio *folio)
{
        if (!folio_test_locked(folio) && !folio_test_dirty(folio) &&
            !folio_test_unevictable(folio) && folio_test_lru(folio)) {
                struct pagevec *pvec;
                unsigned long flags;

                folio_get(folio);
                local_lock_irqsave(&lru_rotate.lock, flags);
                pvec = this_cpu_ptr(&lru_rotate.pvec);
                if (pagevec_add_and_need_flush(pvec, &folio->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_folio(struct folio *folio)
{
        lru_note_cost(folio_lruvec(folio), folio_is_file_lru(folio),
                        folio_nr_pages(folio));
}

static void __folio_activate(struct folio *folio, struct lruvec *lruvec)
{
        if (!folio_test_active(folio) && !folio_test_unevictable(folio)) {
                long nr_pages = folio_nr_pages(folio);

                lruvec_del_folio(lruvec, folio);
                folio_set_active(folio);
                lruvec_add_folio(lruvec, folio);
                trace_mm_lru_activate(folio);

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

#ifdef CONFIG_SMP
static void __activate_page(struct page *page, struct lruvec *lruvec)
{
        return __folio_activate(page_folio(page), lruvec);
}

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 folio_activate(struct folio *folio)
{
        if (folio_test_lru(folio) && !folio_test_active(folio) &&
            !folio_test_unevictable(folio)) {
                struct pagevec *pvec;

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

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

static void folio_activate(struct folio *folio)
{
        struct lruvec *lruvec;

        if (folio_test_clear_lru(folio)) {
                lruvec = folio_lruvec_lock_irq(folio);
                __folio_activate(folio, lruvec);
                unlock_page_lruvec_irq(lruvec);
                folio_set_lru(folio);
        }
}
#endif

static void __lru_cache_activate_folio(struct folio *folio)
{
        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 == &folio->page) {
                        folio_set_active(folio);
                        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 folio_mark_accessed(struct folio *folio)
{
        if (!folio_test_referenced(folio)) {
                folio_set_referenced(folio);
        } else if (folio_test_unevictable(folio)) {
                /*
                 * Unevictable pages are on the "LRU_UNEVICTABLE" list. But,
                 * this list is never rotated or maintained, so marking an
                 * unevictable page accessed has no effect.
                 */
        } else if (!folio_test_active(folio)) {
                /*
                 * 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 (folio_test_lru(folio))
                        folio_activate(folio);
                else
                        __lru_cache_activate_folio(folio);
                folio_clear_referenced(folio);
                workingset_activation(folio);
        }
        if (folio_test_idle(folio))
                folio_clear_idle(folio);
}
EXPORT_SYMBOL(folio_mark_accessed);

/**
 * folio_add_lru - Add a folio to an LRU list.
 * @folio: The folio to be added to the LRU.
 *
 * Queue the folio for addition to the LRU. 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 folio_add_lru()
 * have the folio added to the active list using folio_mark_accessed().
 */
void folio_add_lru(struct folio *folio)
{
        struct pagevec *pvec;

        VM_BUG_ON_FOLIO(folio_test_active(folio) && folio_test_unevictable(folio), folio);
        VM_BUG_ON_FOLIO(folio_test_lru(folio), folio);

        folio_get(folio);
        local_lock(&lru_pvecs.lock);
        pvec = this_cpu_ptr(&lru_pvecs.lru_add);
        if (pagevec_add_and_need_flush(pvec, &folio->page))
                __pagevec_lru_add(pvec);
        local_unlock(&lru_pvecs.lock);
}
EXPORT_SYMBOL(folio_add_lru);

/**
 * 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)
{
        VM_BUG_ON_PAGE(PageLRU(page), page);

        if (unlikely((vma->vm_flags & (VM_LOCKED | VM_SPECIAL)) == VM_LOCKED))
                mlock_new_page(page);
        else
                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_folio() - Forcefully deactivate a file folio.
 * @folio: Folio to deactivate.
 *
 * This function hints to the VM that @folio is a good reclaim candidate,
 * for example if its invalidation fails due to the folio being dirty
 * or under writeback.
 *
 * Context: Caller holds a reference on the page.
 */
void deactivate_file_folio(struct folio *folio)
{
        struct pagevec *pvec;

        /*
         * In a workload with many unevictable pages such as mprotect,
         * unevictable folio deactivation for accelerating reclaim is pointless.
         */
        if (folio_test_unevictable(folio))
                return;

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

        if (pagevec_add_and_need_flush(pvec, &folio->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);
        mlock_page_drain_local();
}

/*
 * 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();
        mlock_page_drain_local();
}

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);
        mlock_page_drain_local();
}

#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.
 */
static 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 (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) ||
                    need_mlock_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);
        /*
         * Readers of lru_disable_count are protected by either disabling
         * preemption or rcu_read_lock:
         *
         * preempt_disable, local_irq_disable  [bh_lru_lock()]
         * rcu_read_lock                       [rt_spin_lock CONFIG_PREEMPT_RT]
         * preempt_disable                     [local_lock !CONFIG_PREEMPT_RT]
         *
         * Since v5.1 kernel, synchronize_rcu() is guaranteed to wait on
         * preempt_disable() regions of code. So any CPU which sees
         * lru_disable_count = 0 will have exited the critical
         * section when synchronize_rcu() returns.
         */
        synchronize_rcu_expedited();
#ifdef CONFIG_SMP
        __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 = 0;
        unsigned int lock_batch;

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

                /*
                 * 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 = &folio->page;
                if (is_huge_zero_page(page))
                        continue;

                if (is_zone_device_page(page)) {
                        if (lruvec) {
                                unlock_page_lruvec_irqrestore(lruvec, flags);
                                lruvec = NULL;
                        }
                        if (put_devmap_managed_page(page))
                                continue;
                        if (put_page_testzero(page))
                                free_zone_device_page(page);
                        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 = folio_lruvec_relock_irqsave(folio, lruvec,
                                                                        &flags);
                        if (prev_lruvec != lruvec)
                                lock_batch = 0;

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

                /*
                 * In rare cases, when truncation or holepunching raced with
                 * munlock after VM_LOCKED was cleared, Mlocked may still be
                 * found set here.  This does not indicate a problem, unless
                 * "unevictable_pgs_cleared" appears worryingly large.
                 */
                if (unlikely(PageMlocked(page))) {
                        __ClearPageMlocked(page);
                        dec_zone_page_state(page, NR_MLOCK);
                        count_vm_event(UNEVICTABLE_PGCLEARED);
                }

                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 folio *folio, struct lruvec *lruvec)
{
        int was_unevictable = folio_test_clear_unevictable(folio);
        long nr_pages = folio_nr_pages(folio);

        VM_BUG_ON_FOLIO(folio_test_lru(folio), folio);

        folio_set_lru(folio);
        /*
         * Is an smp_mb__after_atomic() still required here, before
         * folio_evictable() tests PageMlocked, to rule out the possibility
         * of stranding an evictable folio on an unevictable LRU?  I think
         * not, because __munlock_page() only clears PageMlocked while the LRU
         * lock is held.
         *
         * (That is not true of __page_cache_release(), and not necessarily
         * true of release_pages(): but those only clear PageMlocked after
         * put_page_testzero() has excluded any other users of the page.)
         */
        if (folio_evictable(folio)) {
                if (was_unevictable)
                        __count_vm_events(UNEVICTABLE_PGRESCUED, nr_pages);
        } else {
                folio_clear_active(folio);
                folio_set_unevictable(folio);
                /*
                 * folio->mlock_count = !!folio_test_mlocked(folio)?
                 * But that leaves __mlock_page() in doubt whether another
                 * actor has already counted the mlock or not.  Err on the
                 * safe side, underestimate, let page reclaim fix it, rather
                 * than leaving a page on the unevictable LRU indefinitely.
                 */
                folio->mlock_count = 0;
                if (!was_unevictable)
                        __count_vm_events(UNEVICTABLE_PGCULLED, nr_pages);
        }

        lruvec_add_folio(lruvec, folio);
        trace_mm_lru_insertion(folio);
}

/*
 * 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 folio *folio = page_folio(pvec->pages[i]);

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

/**
 * folio_batch_remove_exceptionals() - Prune non-folios from a batch.
 * @fbatch: The batch to prune
 *
 * find_get_entries() fills a batch with both folios and shadow/swap/DAX
 * entries.  This function prunes all the non-folio entries from @fbatch
 * without leaving holes, so that it can be passed on to folio-only batch
 * operations.
 */
void folio_batch_remove_exceptionals(struct folio_batch *fbatch)
{
        unsigned int i, j;

        for (i = 0, j = 0; i < folio_batch_count(fbatch); i++) {
                struct folio *folio = fbatch->folios[i];
                if (!xa_is_value(folio))
                        fbatch->folios[j++] = folio;
        }
        fbatch->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
         */
}