compaction.c

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/*
 * linux/mm/compaction.c
 *
 * Memory compaction for the reduction of external fragmentation. Note that
 * this heavily depends upon page migration to do all the real heavy
 * lifting
 *
 * Copyright IBM Corp. 2007-2010 Mel Gorman <[email protected]>
 */
#include <linux/swap.h>
#include <linux/migrate.h>
#include <linux/compaction.h>
#include <linux/mm_inline.h>
#include <linux/backing-dev.h>
#include <linux/sysctl.h>
#include <linux/sysfs.h>
#include "internal.h"

#if defined CONFIG_COMPACTION || defined CONFIG_CMA

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

static unsigned long release_freepages(struct list_head *freelist)
{
    struct page *page, *next;
    unsigned long count = 0;

    list_for_each_entry_safe(page, next, freelist, lru) {
        list_del(&page->lru);
        __free_page(page);
        count++;
    }

    return count;
}

static void map_pages(struct list_head *list)
{
    struct page *page;

    list_for_each_entry(page, list, lru) {
        arch_alloc_page(page, 0);
        kernel_map_pages(page, 1, 1);
    }
}

static inline bool migrate_async_suitable(int migratetype)
{
    return is_migrate_cma(migratetype) || migratetype == MIGRATE_MOVABLE;
}

#ifdef CONFIG_COMPACTION
/* Returns true if the pageblock should be scanned for pages to isolate. */
static inline bool isolation_suitable(struct compact_control *cc,
                    struct page *page)
{
    if (cc->ignore_skip_hint)
        return true;

    return !get_pageblock_skip(page);
}

/*
 * This function is called to clear all cached information on pageblocks that
 * should be skipped for page isolation when the migrate and free page scanner
 * meet.
 */
static void __reset_isolation_suitable(struct zone *zone)
{
    unsigned long start_pfn = zone->zone_start_pfn;
    unsigned long end_pfn = zone->zone_start_pfn + zone->spanned_pages;
    unsigned long pfn;

    zone->compact_cached_migrate_pfn = start_pfn;
    zone->compact_cached_free_pfn = end_pfn;
    zone->compact_blockskip_flush = false;

    /* Walk the zone and mark every pageblock as suitable for isolation */
    for (pfn = start_pfn; pfn < end_pfn; pfn += pageblock_nr_pages) {
        struct page *page;

        cond_resched();

        if (!pfn_valid(pfn))
            continue;

        page = pfn_to_page(pfn);
        if (zone != page_zone(page))
            continue;

        clear_pageblock_skip(page);
    }
}

void reset_isolation_suitable(pg_data_t *pgdat)
{
    int zoneid;

    for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
        struct zone *zone = &pgdat->node_zones[zoneid];
        if (!populated_zone(zone))
            continue;

        /* Only flush if a full compaction finished recently */
        if (zone->compact_blockskip_flush)
            __reset_isolation_suitable(zone);
    }
}

/*
 * If no pages were isolated then mark this pageblock to be skipped in the
 * future. The information is later cleared by __reset_isolation_suitable().
 */
static void update_pageblock_skip(struct compact_control *cc,
            struct page *page, unsigned long nr_isolated,
            bool migrate_scanner)
{
    struct zone *zone = cc->zone;
    if (!page)
        return;

    if (!nr_isolated) {
        unsigned long pfn = page_to_pfn(page);
        set_pageblock_skip(page);

        /* Update where compaction should restart */
        if (migrate_scanner) {
            if (!cc->finished_update_migrate &&
                pfn > zone->compact_cached_migrate_pfn)
                zone->compact_cached_migrate_pfn = pfn;
        } else {
            if (!cc->finished_update_free &&
                pfn < zone->compact_cached_free_pfn)
                zone->compact_cached_free_pfn = pfn;
        }
    }
}
#else
static inline bool isolation_suitable(struct compact_control *cc,
                    struct page *page)
{
    return true;
}

static void update_pageblock_skip(struct compact_control *cc,
            struct page *page, unsigned long nr_isolated,
            bool migrate_scanner)
{
}
#endif /* CONFIG_COMPACTION */

static inline bool should_release_lock(spinlock_t *lock)
{
    return need_resched() || spin_is_contended(lock);
}

/*
 * Compaction requires the taking of some coarse locks that are potentially
 * very heavily contended. Check if the process needs to be scheduled or
 * if the lock is contended. For async compaction, back out in the event
 * if contention is severe. For sync compaction, schedule.
 *
 * Returns true if the lock is held.
 * Returns false if the lock is released and compaction should abort
 */
static bool compact_checklock_irqsave(spinlock_t *lock, unsigned long *flags,
                      bool locked, struct compact_control *cc)
{
    if (should_release_lock(lock)) {
        if (locked) {
            spin_unlock_irqrestore(lock, *flags);
            locked = false;
        }

        /* async aborts if taking too long or contended */
        if (!cc->sync) {
            cc->contended = true;
            return false;
        }

        cond_resched();
    }

    if (!locked)
        spin_lock_irqsave(lock, *flags);
    return true;
}

static inline bool compact_trylock_irqsave(spinlock_t *lock,
            unsigned long *flags, struct compact_control *cc)
{
    return compact_checklock_irqsave(lock, flags, false, cc);
}

/* Returns true if the page is within a block suitable for migration to */
static bool suitable_migration_target(struct page *page)
{
    int migratetype = get_pageblock_migratetype(page);

    /* Don't interfere with memory hot-remove or the min_free_kbytes blocks */
    if (migratetype == MIGRATE_ISOLATE || migratetype == MIGRATE_RESERVE)
        return false;

    /* If the page is a large free page, then allow migration */
    if (PageBuddy(page) && page_order(page) >= pageblock_order)
        return true;

    /* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */
    if (migrate_async_suitable(migratetype))
        return true;

    /* Otherwise skip the block */
    return false;
}

static void compact_capture_page(struct compact_control *cc)
{
    unsigned long flags;
    int mtype, mtype_low, mtype_high;

    if (!cc->page || *cc->page)
        return;

    /*
     * For MIGRATE_MOVABLE allocations we capture a suitable page ASAP
     * regardless of the migratetype of the freelist is is captured from.
     * This is fine because the order for a high-order MIGRATE_MOVABLE
     * allocation is typically at least a pageblock size and overall
     * fragmentation is not impaired. Other allocation types must
     * capture pages from their own migratelist because otherwise they
     * could pollute other pageblocks like MIGRATE_MOVABLE with
     * difficult to move pages and making fragmentation worse overall.
     */
    if (cc->migratetype == MIGRATE_MOVABLE) {
        mtype_low = 0;
        mtype_high = MIGRATE_PCPTYPES;
    } else {
        mtype_low = cc->migratetype;
        mtype_high = cc->migratetype + 1;
    }

    /* Speculatively examine the free lists without zone lock */
    for (mtype = mtype_low; mtype < mtype_high; mtype++) {
        int order;
        for (order = cc->order; order < MAX_ORDER; order++) {
            struct page *page;
            struct free_area *area;
            area = &(cc->zone->free_area[order]);
            if (list_empty(&area->free_list[mtype]))
                continue;

            /* Take the lock and attempt capture of the page */
            if (!compact_trylock_irqsave(&cc->zone->lock, &flags, cc))
                return;
            if (!list_empty(&area->free_list[mtype])) {
                page = list_entry(area->free_list[mtype].next,
                            struct page, lru);
                if (capture_free_page(page, cc->order, mtype)) {
                    spin_unlock_irqrestore(&cc->zone->lock,
                                    flags);
                    *cc->page = page;
                    return;
                }
            }
            spin_unlock_irqrestore(&cc->zone->lock, flags);
        }
    }
}

/*
 * Isolate free pages onto a private freelist. Caller must hold zone->lock.
 * If @strict is true, will abort returning 0 on any invalid PFNs or non-free
 * pages inside of the pageblock (even though it may still end up isolating
 * some pages).
 */
static unsigned long isolate_freepages_block(struct compact_control *cc,
                unsigned long blockpfn,
                unsigned long end_pfn,
                struct list_head *freelist,
                bool strict)
{
    int nr_scanned = 0, total_isolated = 0;
    struct page *cursor, *valid_page = NULL;
    unsigned long nr_strict_required = end_pfn - blockpfn;
    unsigned long flags;
    bool locked = false;

    cursor = pfn_to_page(blockpfn);

    /* Isolate free pages. */
    for (; blockpfn < end_pfn; blockpfn++, cursor++) {
        int isolated, i;
        struct page *page = cursor;

        nr_scanned++;
        if (!pfn_valid_within(blockpfn))
            continue;
        if (!valid_page)
            valid_page = page;
        if (!PageBuddy(page))
            continue;

        /*
         * The zone lock must be held to isolate freepages.
         * Unfortunately this is a very coarse lock and can be
         * heavily contended if there are parallel allocations
         * or parallel compactions. For async compaction do not
         * spin on the lock and we acquire the lock as late as
         * possible.
         */
        locked = compact_checklock_irqsave(&cc->zone->lock, &flags,
                                locked, cc);
        if (!locked)
            break;

        /* Recheck this is a suitable migration target under lock */
        if (!strict && !suitable_migration_target(page))
            break;

        /* Recheck this is a buddy page under lock */
        if (!PageBuddy(page))
            continue;

        /* Found a free page, break it into order-0 pages */
        isolated = split_free_page(page);
        if (!isolated && strict)
            break;
        total_isolated += isolated;
        for (i = 0; i < isolated; i++) {
            list_add(&page->lru, freelist);
            page++;
        }

        /* If a page was split, advance to the end of it */
        if (isolated) {
            blockpfn += isolated - 1;
            cursor += isolated - 1;
        }
    }

    trace_mm_compaction_isolate_freepages(nr_scanned, total_isolated);

    /*
     * If strict isolation is requested by CMA then check that all the
     * pages requested were isolated. If there were any failures, 0 is
     * returned and CMA will fail.
     */
    if (strict && nr_strict_required > total_isolated)
        total_isolated = 0;

    if (locked)
        spin_unlock_irqrestore(&cc->zone->lock, flags);

    /* Update the pageblock-skip if the whole pageblock was scanned */
    if (blockpfn == end_pfn)
        update_pageblock_skip(cc, valid_page, total_isolated, false);

    return total_isolated;
}

unsigned long
isolate_freepages_range(struct compact_control *cc,
            unsigned long start_pfn, unsigned long end_pfn)
{
    unsigned long isolated, pfn, block_end_pfn;
    LIST_HEAD(freelist);

    for (pfn = start_pfn; pfn < end_pfn; pfn += isolated) {
        if (!pfn_valid(pfn) || cc->zone != page_zone(pfn_to_page(pfn)))
            break;

        /*
         * On subsequent iterations ALIGN() is actually not needed,
         * but we keep it that we not to complicate the code.
         */
        block_end_pfn = ALIGN(pfn + 1, pageblock_nr_pages);
        block_end_pfn = min(block_end_pfn, end_pfn);

        isolated = isolate_freepages_block(cc, pfn, block_end_pfn,
                           &freelist, true);

        /*
         * In strict mode, isolate_freepages_block() returns 0 if
         * there are any holes in the block (ie. invalid PFNs or
         * non-free pages).
         */
        if (!isolated)
            break;

        /*
         * If we managed to isolate pages, it is always (1 << n) *
         * pageblock_nr_pages for some non-negative n.  (Max order
         * page may span two pageblocks).
         */
    }

    /* split_free_page does not map the pages */
    map_pages(&freelist);

    if (pfn < end_pfn) {
        /* Loop terminated early, cleanup. */
        release_freepages(&freelist);
        return 0;
    }

    /* We don't use freelists for anything. */
    return pfn;
}

/* Update the number of anon and file isolated pages in the zone */
static void acct_isolated(struct zone *zone, bool locked, struct compact_control *cc)
{
    struct page *page;
    unsigned int count[2] = { 0, };

    list_for_each_entry(page, &cc->migratepages, lru)
        count[!!page_is_file_cache(page)]++;

    /* If locked we can use the interrupt unsafe versions */
    if (locked) {
        __mod_zone_page_state(zone, NR_ISOLATED_ANON, count[0]);
        __mod_zone_page_state(zone, NR_ISOLATED_FILE, count[1]);
    } else {
        mod_zone_page_state(zone, NR_ISOLATED_ANON, count[0]);
        mod_zone_page_state(zone, NR_ISOLATED_FILE, count[1]);
    }
}

/* Similar to reclaim, but different enough that they don't share logic */
static bool too_many_isolated(struct zone *zone)
{
    unsigned long active, inactive, isolated;

    inactive = zone_page_state(zone, NR_INACTIVE_FILE) +
                    zone_page_state(zone, NR_INACTIVE_ANON);
    active = zone_page_state(zone, NR_ACTIVE_FILE) +
                    zone_page_state(zone, NR_ACTIVE_ANON);
    isolated = zone_page_state(zone, NR_ISOLATED_FILE) +
                    zone_page_state(zone, NR_ISOLATED_ANON);

    return isolated > (inactive + active) / 2;
}

unsigned long
isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
        unsigned long low_pfn, unsigned long end_pfn, bool unevictable)
{
    unsigned long last_pageblock_nr = 0, pageblock_nr;
    unsigned long nr_scanned = 0, nr_isolated = 0;
    struct list_head *migratelist = &cc->migratepages;
    isolate_mode_t mode = 0;
    struct lruvec *lruvec;
    unsigned long flags;
    bool locked = false;
    struct page *page = NULL, *valid_page = NULL;

    /*
     * Ensure that there are not too many pages isolated from the LRU
     * list by either parallel reclaimers or compaction. If there are,
     * delay for some time until fewer pages are isolated
     */
    while (unlikely(too_many_isolated(zone))) {
        /* async migration should just abort */
        if (!cc->sync)
            return 0;

        congestion_wait(BLK_RW_ASYNC, HZ/10);

        if (fatal_signal_pending(current))
            return 0;
    }

    /* Time to isolate some pages for migration */
    cond_resched();
    for (; low_pfn < end_pfn; low_pfn++) {
        /* give a chance to irqs before checking need_resched() */
        if (locked && !((low_pfn+1) % SWAP_CLUSTER_MAX)) {
            if (should_release_lock(&zone->lru_lock)) {
                spin_unlock_irqrestore(&zone->lru_lock, flags);
                locked = false;
            }
        }

        /*
         * migrate_pfn does not necessarily start aligned to a
         * pageblock. Ensure that pfn_valid is called when moving
         * into a new MAX_ORDER_NR_PAGES range in case of large
         * memory holes within the zone
         */
        if ((low_pfn & (MAX_ORDER_NR_PAGES - 1)) == 0) {
            if (!pfn_valid(low_pfn)) {
                low_pfn += MAX_ORDER_NR_PAGES - 1;
                continue;
            }
        }

        if (!pfn_valid_within(low_pfn))
            continue;
        nr_scanned++;

        /*
         * Get the page and ensure the page is within the same zone.
         * See the comment in isolate_freepages about overlapping
         * nodes. It is deliberate that the new zone lock is not taken
         * as memory compaction should not move pages between nodes.
         */
        page = pfn_to_page(low_pfn);
        if (page_zone(page) != zone)
            continue;

        if (!valid_page)
            valid_page = page;

        /* If isolation recently failed, do not retry */
        pageblock_nr = low_pfn >> pageblock_order;
        if (!isolation_suitable(cc, page))
            goto next_pageblock;

        /* Skip if free */
        if (PageBuddy(page))
            continue;

        /*
         * For async migration, also only scan in MOVABLE blocks. Async
         * migration is optimistic to see if the minimum amount of work
         * satisfies the allocation
         */
        if (!cc->sync && last_pageblock_nr != pageblock_nr &&
            !migrate_async_suitable(get_pageblock_migratetype(page))) {
            cc->finished_update_migrate = true;
            goto next_pageblock;
        }

        /* Check may be lockless but that's ok as we recheck later */
        if (!PageLRU(page))
            continue;

        /*
         * PageLRU is set. lru_lock normally excludes isolation
         * splitting and collapsing (collapsing has already happened
         * if PageLRU is set) but the lock is not necessarily taken
         * here and it is wasteful to take it just to check transhuge.
         * Check TransHuge without lock and skip the whole pageblock if
         * it's either a transhuge or hugetlbfs page, as calling
         * compound_order() without preventing THP from splitting the
         * page underneath us may return surprising results.
         */
        if (PageTransHuge(page)) {
            if (!locked)
                goto next_pageblock;
            low_pfn += (1 << compound_order(page)) - 1;
            continue;
        }

        /* Check if it is ok to still hold the lock */
        locked = compact_checklock_irqsave(&zone->lru_lock, &flags,
                                locked, cc);
        if (!locked || fatal_signal_pending(current))
            break;

        /* Recheck PageLRU and PageTransHuge under lock */
        if (!PageLRU(page))
            continue;
        if (PageTransHuge(page)) {
            low_pfn += (1 << compound_order(page)) - 1;
            continue;
        }

        if (!cc->sync)
            mode |= ISOLATE_ASYNC_MIGRATE;

        if (unevictable)
            mode |= ISOLATE_UNEVICTABLE;

        lruvec = mem_cgroup_page_lruvec(page, zone);

        /* Try isolate the page */
        if (__isolate_lru_page(page, mode) != 0)
            continue;

        VM_BUG_ON(PageTransCompound(page));

        /* Successfully isolated */
        cc->finished_update_migrate = true;
        del_page_from_lru_list(page, lruvec, page_lru(page));
        list_add(&page->lru, migratelist);
        cc->nr_migratepages++;
        nr_isolated++;

        /* Avoid isolating too much */
        if (cc->nr_migratepages == COMPACT_CLUSTER_MAX) {
            ++low_pfn;
            break;
        }

        continue;

next_pageblock:
        low_pfn += pageblock_nr_pages;
        low_pfn = ALIGN(low_pfn, pageblock_nr_pages) - 1;
        last_pageblock_nr = pageblock_nr;
    }

    acct_isolated(zone, locked, cc);

    if (locked)
        spin_unlock_irqrestore(&zone->lru_lock, flags);

    /* Update the pageblock-skip if the whole pageblock was scanned */
    if (low_pfn == end_pfn)
        update_pageblock_skip(cc, valid_page, nr_isolated, true);

    trace_mm_compaction_isolate_migratepages(nr_scanned, nr_isolated);

    return low_pfn;
}

#endif /* CONFIG_COMPACTION || CONFIG_CMA */
#ifdef CONFIG_COMPACTION
/*
 * Based on information in the current compact_control, find blocks
 * suitable for isolating free pages from and then isolate them.
 */
static void isolate_freepages(struct zone *zone,
                struct compact_control *cc)
{
    struct page *page;
    unsigned long high_pfn, low_pfn, pfn, zone_end_pfn, end_pfn;
    int nr_freepages = cc->nr_freepages;
    struct list_head *freelist = &cc->freepages;

    /*
     * Initialise the free scanner. The starting point is where we last
     * scanned from (or the end of the zone if starting). The low point
     * is the end of the pageblock the migration scanner is using.
     */
    pfn = cc->free_pfn;
    low_pfn = cc->migrate_pfn + pageblock_nr_pages;

    /*
     * Take care that if the migration scanner is at the end of the zone
     * that the free scanner does not accidentally move to the next zone
     * in the next isolation cycle.
     */
    high_pfn = min(low_pfn, pfn);

    zone_end_pfn = zone->zone_start_pfn + zone->spanned_pages;

    /*
     * Isolate free pages until enough are available to migrate the
     * pages on cc->migratepages. We stop searching if the migrate
     * and free page scanners meet or enough free pages are isolated.
     */
    for (; pfn > low_pfn && cc->nr_migratepages > nr_freepages;
                    pfn -= pageblock_nr_pages) {
        unsigned long isolated;

        if (!pfn_valid(pfn))
            continue;

        /*
         * Check for overlapping nodes/zones. It's possible on some
         * configurations to have a setup like
         * node0 node1 node0
         * i.e. it's possible that all pages within a zones range of
         * pages do not belong to a single zone.
         */
        page = pfn_to_page(pfn);
        if (page_zone(page) != zone)
            continue;

        /* Check the block is suitable for migration */
        if (!suitable_migration_target(page))
            continue;

        /* If isolation recently failed, do not retry */
        if (!isolation_suitable(cc, page))
            continue;

        /* Found a block suitable for isolating free pages from */
        isolated = 0;

        /*
         * As pfn may not start aligned, pfn+pageblock_nr_page
         * may cross a MAX_ORDER_NR_PAGES boundary and miss
         * a pfn_valid check. Ensure isolate_freepages_block()
         * only scans within a pageblock
         */
        end_pfn = ALIGN(pfn + 1, pageblock_nr_pages);
        end_pfn = min(end_pfn, zone_end_pfn);
        isolated = isolate_freepages_block(cc, pfn, end_pfn,
                           freelist, false);
        nr_freepages += isolated;

        /*
         * Record the highest PFN we isolated pages from. When next
         * looking for free pages, the search will restart here as
         * page migration may have returned some pages to the allocator
         */
        if (isolated) {
            cc->finished_update_free = true;
            high_pfn = max(high_pfn, pfn);
        }
    }

    /* split_free_page does not map the pages */
    map_pages(freelist);

    cc->free_pfn = high_pfn;
    cc->nr_freepages = nr_freepages;
}

/*
 * This is a migrate-callback that "allocates" freepages by taking pages
 * from the isolated freelists in the block we are migrating to.
 */
static struct page *compaction_alloc(struct page *migratepage,
                    unsigned long data,
                    int **result)
{
    struct compact_control *cc = (struct compact_control *)data;
    struct page *freepage;

    /* Isolate free pages if necessary */
    if (list_empty(&cc->freepages)) {
        isolate_freepages(cc->zone, cc);

        if (list_empty(&cc->freepages))
            return NULL;
    }

    freepage = list_entry(cc->freepages.next, struct page, lru);
    list_del(&freepage->lru);
    cc->nr_freepages--;

    return freepage;
}

/*
 * We cannot control nr_migratepages and nr_freepages fully when migration is
 * running as migrate_pages() has no knowledge of compact_control. When
 * migration is complete, we count the number of pages on the lists by hand.
 */
static void update_nr_listpages(struct compact_control *cc)
{
    int nr_migratepages = 0;
    int nr_freepages = 0;
    struct page *page;

    list_for_each_entry(page, &cc->migratepages, lru)
        nr_migratepages++;
    list_for_each_entry(page, &cc->freepages, lru)
        nr_freepages++;

    cc->nr_migratepages = nr_migratepages;
    cc->nr_freepages = nr_freepages;
}

/* possible outcome of isolate_migratepages */
typedef enum {
    ISOLATE_ABORT,      /* Abort compaction now */
    ISOLATE_NONE,       /* No pages isolated, continue scanning */
    ISOLATE_SUCCESS,    /* Pages isolated, migrate */
} isolate_migrate_t;

/*
 * Isolate all pages that can be migrated from the block pointed to by
 * the migrate scanner within compact_control.
 */
static isolate_migrate_t isolate_migratepages(struct zone *zone,
                    struct compact_control *cc)
{
    unsigned long low_pfn, end_pfn;

    /* Do not scan outside zone boundaries */
    low_pfn = max(cc->migrate_pfn, zone->zone_start_pfn);

    /* Only scan within a pageblock boundary */
    end_pfn = ALIGN(low_pfn + pageblock_nr_pages, pageblock_nr_pages);

    /* Do not cross the free scanner or scan within a memory hole */
    if (end_pfn > cc->free_pfn || !pfn_valid(low_pfn)) {
        cc->migrate_pfn = end_pfn;
        return ISOLATE_NONE;
    }

    /* Perform the isolation */
    low_pfn = isolate_migratepages_range(zone, cc, low_pfn, end_pfn, false);
    if (!low_pfn || cc->contended)
        return ISOLATE_ABORT;

    cc->migrate_pfn = low_pfn;

    return ISOLATE_SUCCESS;
}

static int compact_finished(struct zone *zone,
                struct compact_control *cc)
{
    unsigned long watermark;

    if (fatal_signal_pending(current))
        return COMPACT_PARTIAL;

    /* Compaction run completes if the migrate and free scanner meet */
    if (cc->free_pfn <= cc->migrate_pfn) {
        /*
         * Mark that the PG_migrate_skip information should be cleared
         * by kswapd when it goes to sleep. kswapd does not set the
         * flag itself as the decision to be clear should be directly
         * based on an allocation request.
         */
        if (!current_is_kswapd())
            zone->compact_blockskip_flush = true;

        return COMPACT_COMPLETE;
    }

    /*
     * order == -1 is expected when compacting via
     * /proc/sys/vm/compact_memory
     */
    if (cc->order == -1)
        return COMPACT_CONTINUE;

    /* Compaction run is not finished if the watermark is not met */
    watermark = low_wmark_pages(zone);
    watermark += (1 << cc->order);

    if (!zone_watermark_ok(zone, cc->order, watermark, 0, 0))
        return COMPACT_CONTINUE;

    /* Direct compactor: Is a suitable page free? */
    if (cc->page) {
        /* Was a suitable page captured? */
        if (*cc->page)
            return COMPACT_PARTIAL;
    } else {
        unsigned int order;
        for (order = cc->order; order < MAX_ORDER; order++) {
            struct free_area *area = &zone->free_area[cc->order];
            /* Job done if page is free of the right migratetype */
            if (!list_empty(&area->free_list[cc->migratetype]))
                return COMPACT_PARTIAL;

            /* Job done if allocation would set block type */
            if (cc->order >= pageblock_order && area->nr_free)
                return COMPACT_PARTIAL;
        }
    }

    return COMPACT_CONTINUE;
}

/*
 * compaction_suitable: Is this suitable to run compaction on this zone now?
 * Returns
 *   COMPACT_SKIPPED  - If there are too few free pages for compaction
 *   COMPACT_PARTIAL  - If the allocation would succeed without compaction
 *   COMPACT_CONTINUE - If compaction should run now
 */
unsigned long compaction_suitable(struct zone *zone, int order)
{
    int fragindex;
    unsigned long watermark;

    /*
     * order == -1 is expected when compacting via
     * /proc/sys/vm/compact_memory
     */
    if (order == -1)
        return COMPACT_CONTINUE;

    /*
     * Watermarks for order-0 must be met for compaction. Note the 2UL.
     * This is because during migration, copies of pages need to be
     * allocated and for a short time, the footprint is higher
     */
    watermark = low_wmark_pages(zone) + (2UL << order);
    if (!zone_watermark_ok(zone, 0, watermark, 0, 0))
        return COMPACT_SKIPPED;

    /*
     * fragmentation index determines if allocation failures are due to
     * low memory or external fragmentation
     *
     * index of -1000 implies allocations might succeed depending on
     * watermarks
     * index towards 0 implies failure is due to lack of memory
     * index towards 1000 implies failure is due to fragmentation
     *
     * Only compact if a failure would be due to fragmentation.
     */
    fragindex = fragmentation_index(zone, order);
    if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold)
        return COMPACT_SKIPPED;

    if (fragindex == -1000 && zone_watermark_ok(zone, order, watermark,
        0, 0))
        return COMPACT_PARTIAL;

    return COMPACT_CONTINUE;
}

static int compact_zone(struct zone *zone, struct compact_control *cc)
{
    int ret;
    unsigned long start_pfn = zone->zone_start_pfn;
    unsigned long end_pfn = zone->zone_start_pfn + zone->spanned_pages;

    ret = compaction_suitable(zone, cc->order);
    switch (ret) {
    case COMPACT_PARTIAL:
    case COMPACT_SKIPPED:
        /* Compaction is likely to fail */
        return ret;
    case COMPACT_CONTINUE:
        /* Fall through to compaction */
        ;
    }

    /*
     * Setup to move all movable pages to the end of the zone. Used cached
     * information on where the scanners should start but check that it
     * is initialised by ensuring the values are within zone boundaries.
     */
    cc->migrate_pfn = zone->compact_cached_migrate_pfn;
    cc->free_pfn = zone->compact_cached_free_pfn;
    if (cc->free_pfn < start_pfn || cc->free_pfn > end_pfn) {
        cc->free_pfn = end_pfn & ~(pageblock_nr_pages-1);
        zone->compact_cached_free_pfn = cc->free_pfn;
    }
    if (cc->migrate_pfn < start_pfn || cc->migrate_pfn > end_pfn) {
        cc->migrate_pfn = start_pfn;
        zone->compact_cached_migrate_pfn = cc->migrate_pfn;
    }

    /*
     * Clear pageblock skip if there were failures recently and compaction
     * is about to be retried after being deferred. kswapd does not do
     * this reset as it'll reset the cached information when going to sleep.
     */
    if (compaction_restarting(zone, cc->order) && !current_is_kswapd())
        __reset_isolation_suitable(zone);

    migrate_prep_local();

    while ((ret = compact_finished(zone, cc)) == COMPACT_CONTINUE) {
        unsigned long nr_migrate, nr_remaining;
        int err;

        switch (isolate_migratepages(zone, cc)) {
        case ISOLATE_ABORT:
            ret = COMPACT_PARTIAL;
            putback_lru_pages(&cc->migratepages);
            cc->nr_migratepages = 0;
            goto out;
        case ISOLATE_NONE:
            continue;
        case ISOLATE_SUCCESS:
            ;
        }

        nr_migrate = cc->nr_migratepages;
        err = migrate_pages(&cc->migratepages, compaction_alloc,
                (unsigned long)cc, false,
                cc->sync ? MIGRATE_SYNC_LIGHT : MIGRATE_ASYNC);
        update_nr_listpages(cc);
        nr_remaining = cc->nr_migratepages;

        count_vm_event(COMPACTBLOCKS);
        count_vm_events(COMPACTPAGES, nr_migrate - nr_remaining);
        if (nr_remaining)
            count_vm_events(COMPACTPAGEFAILED, nr_remaining);
        trace_mm_compaction_migratepages(nr_migrate - nr_remaining,
                        nr_remaining);

        /* Release LRU pages not migrated */
        if (err) {
            putback_lru_pages(&cc->migratepages);
            cc->nr_migratepages = 0;
            if (err == -ENOMEM) {
                ret = COMPACT_PARTIAL;
                goto out;
            }
        }

        /* Capture a page now if it is a suitable size */
        compact_capture_page(cc);
    }

out:
    /* Release free pages and check accounting */
    cc->nr_freepages -= release_freepages(&cc->freepages);
    VM_BUG_ON(cc->nr_freepages != 0);

    return ret;
}

static unsigned long compact_zone_order(struct zone *zone,
                 int order, gfp_t gfp_mask,
                 bool sync, bool *contended,
                 struct page **page)
{
    unsigned long ret;
    struct compact_control cc = {
        .nr_freepages = 0,
        .nr_migratepages = 0,
        .order = order,
        .migratetype = allocflags_to_migratetype(gfp_mask),
        .zone = zone,
        .sync = sync,
        .page = page,
    };
    INIT_LIST_HEAD(&cc.freepages);
    INIT_LIST_HEAD(&cc.migratepages);

    ret = compact_zone(zone, &cc);

    VM_BUG_ON(!list_empty(&cc.freepages));
    VM_BUG_ON(!list_empty(&cc.migratepages));

    *contended = cc.contended;
    return ret;
}

int sysctl_extfrag_threshold = 500;

unsigned long try_to_compact_pages(struct zonelist *zonelist,
            int order, gfp_t gfp_mask, nodemask_t *nodemask,
            bool sync, bool *contended, struct page **page)
{
    enum zone_type high_zoneidx = gfp_zone(gfp_mask);
    int may_enter_fs = gfp_mask & __GFP_FS;
    int may_perform_io = gfp_mask & __GFP_IO;
    struct zoneref *z;
    struct zone *zone;
    int rc = COMPACT_SKIPPED;
    int alloc_flags = 0;

    /* Check if the GFP flags allow compaction */
    if (!order || !may_enter_fs || !may_perform_io)
        return rc;

    count_vm_event(COMPACTSTALL);

#ifdef CONFIG_CMA
    if (allocflags_to_migratetype(gfp_mask) == MIGRATE_MOVABLE)
        alloc_flags |= ALLOC_CMA;
#endif
    /* Compact each zone in the list */
    for_each_zone_zonelist_nodemask(zone, z, zonelist, high_zoneidx,
                                nodemask) {
        int status;

        status = compact_zone_order(zone, order, gfp_mask, sync,
                        contended, page);
        rc = max(status, rc);

        /* If a normal allocation would succeed, stop compacting */
        if (zone_watermark_ok(zone, order, low_wmark_pages(zone), 0,
                      alloc_flags))
            break;
    }

    return rc;
}


/* Compact all zones within a node */
static int __compact_pgdat(pg_data_t *pgdat, struct compact_control *cc)
{
    int zoneid;
    struct zone *zone;

    for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {

        zone = &pgdat->node_zones[zoneid];
        if (!populated_zone(zone))
            continue;

        cc->nr_freepages = 0;
        cc->nr_migratepages = 0;
        cc->zone = zone;
        INIT_LIST_HEAD(&cc->freepages);
        INIT_LIST_HEAD(&cc->migratepages);

        if (cc->order == -1 || !compaction_deferred(zone, cc->order))
            compact_zone(zone, cc);

        if (cc->order > 0) {
            int ok = zone_watermark_ok(zone, cc->order,
                        low_wmark_pages(zone), 0, 0);
            if (ok && cc->order >= zone->compact_order_failed)
                zone->compact_order_failed = cc->order + 1;
            /* Currently async compaction is never deferred. */
            else if (!ok && cc->sync)
                defer_compaction(zone, cc->order);
        }

        VM_BUG_ON(!list_empty(&cc->freepages));
        VM_BUG_ON(!list_empty(&cc->migratepages));
    }

    return 0;
}

int compact_pgdat(pg_data_t *pgdat, int order)
{
    struct compact_control cc = {
        .order = order,
        .sync = false,
        .page = NULL,
    };

    return __compact_pgdat(pgdat, &cc);
}

static int compact_node(int nid)
{
    struct compact_control cc = {
        .order = -1,
        .sync = true,
        .page = NULL,
    };

    return __compact_pgdat(NODE_DATA(nid), &cc);
}

/* Compact all nodes in the system */
static int compact_nodes(void)
{
    int nid;

    /* Flush pending updates to the LRU lists */
    lru_add_drain_all();

    for_each_online_node(nid)
        compact_node(nid);

    return COMPACT_COMPLETE;
}

/* The written value is actually unused, all memory is compacted */
int sysctl_compact_memory;

/* This is the entry point for compacting all nodes via /proc/sys/vm */
int sysctl_compaction_handler(struct ctl_table *table, int write,
            void __user *buffer, size_t *length, loff_t *ppos)
{
    if (write)
        return compact_nodes();

    return 0;
}

int sysctl_extfrag_handler(struct ctl_table *table, int write,
            void __user *buffer, size_t *length, loff_t *ppos)
{
    proc_dointvec_minmax(table, write, buffer, length, ppos);

    return 0;
}

#if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
ssize_t sysfs_compact_node(struct device *dev,
            struct device_attribute *attr,
            const char *buf, size_t count)
{
    int nid = dev->id;

    if (nid >= 0 && nid < nr_node_ids && node_online(nid)) {
        /* Flush pending updates to the LRU lists */
        lru_add_drain_all();

        compact_node(nid);
    }

    return count;
}
static DEVICE_ATTR(compact, S_IWUSR, NULL, sysfs_compact_node);

int compaction_register_node(struct node *node)
{
    return device_create_file(&node->dev, &dev_attr_compact);
}

void compaction_unregister_node(struct node *node)
{
    return device_remove_file(&node->dev, &dev_attr_compact);
}
#endif /* CONFIG_SYSFS && CONFIG_NUMA */

#endif /* CONFIG_COMPACTION */