mm: compaction: minimise the time IRQs are disabled while isolating free pages

[linux-2.6/next.git] / mm / compaction.c

/*
 * 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 <mel@csn.ul.ie>
 */
#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"

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

/*
 * compact_control is used to track pages being migrated and the free pages
 * they are being migrated to during memory compaction. The free_pfn starts
 * at the end of a zone and migrate_pfn begins at the start. Movable pages
 * are moved to the end of a zone during a compaction run and the run
 * completes when free_pfn <= migrate_pfn
 */
struct compact_control {
        struct list_head freepages;     /* List of free pages to migrate to */
        struct list_head migratepages;  /* List of pages being migrated */
        unsigned long nr_freepages;     /* Number of isolated free pages */
        unsigned long nr_migratepages;  /* Number of pages to migrate */
        unsigned long free_pfn;         /* isolate_freepages search base */
        unsigned long migrate_pfn;      /* isolate_migratepages search base */
        bool sync;                      /* Synchronous migration */

        /* Account for isolated anon and file pages */
        unsigned long nr_anon;
        unsigned long nr_file;

        unsigned int order;             /* order a direct compactor needs */
        int migratetype;                /* MOVABLE, RECLAIMABLE etc */
        struct zone *zone;
};

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;
}

/* Isolate free pages onto a private freelist. Must hold zone->lock */
static unsigned long isolate_freepages_block(struct zone *zone,
                                unsigned long blockpfn,
                                struct list_head *freelist)
{
        unsigned long zone_end_pfn, end_pfn;
        int nr_scanned = 0, total_isolated = 0;
        struct page *cursor;

        /* Get the last PFN we should scan for free pages at */
        zone_end_pfn = zone->zone_start_pfn + zone->spanned_pages;
        end_pfn = min(blockpfn + pageblock_nr_pages, zone_end_pfn);

        /* Find the first usable PFN in the block to initialse page cursor */
        for (; blockpfn < end_pfn; blockpfn++) {
                if (pfn_valid_within(blockpfn))
                        break;
        }
        cursor = pfn_to_page(blockpfn);

        /* Isolate free pages. This assumes the block is valid */
        for (; blockpfn < end_pfn; blockpfn++, cursor++) {
                int isolated, i;
                struct page *page = cursor;

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

                if (!PageBuddy(page))
                        continue;

                /* Found a free page, break it into order-0 pages */
                isolated = split_free_page(page);
                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);
        return total_isolated;
}

/* 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, allow migration */
        if (migratetype == MIGRATE_MOVABLE)
                return true;

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

/*
 * 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;
        unsigned long flags;
        int nr_freepages = cc->nr_freepages;
        struct list_head *freelist = &cc->freepages;

        pfn = cc->free_pfn;
        low_pfn = cc->migrate_pfn + pageblock_nr_pages;
        high_pfn = low_pfn;

        /*
         * 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;

                /*
                 * Found a block suitable for isolating free pages from. Now
                 * we disabled interrupts, double check things are ok and
                 * isolate the pages. This is to minimise the time IRQs
                 * are disabled
                 */
                isolated = 0;
                spin_lock_irqsave(&zone->lock, flags);
                if (suitable_migration_target(page)) {
                        isolated = isolate_freepages_block(zone, pfn, freelist);
                        nr_freepages += isolated;
                }
                spin_unlock_irqrestore(&zone->lock, flags);

                /*
                 * 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)
                        high_pfn = max(high_pfn, pfn);
        }

        /* split_free_page does not map the pages */
        list_for_each_entry(page, freelist, lru) {
                arch_alloc_page(page, 0);
                kernel_map_pages(page, 1, 1);
        }

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

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

        list_for_each_entry(page, &cc->migratepages, lru) {
                int lru = page_lru_base_type(page);
                count[lru]++;
        }

        cc->nr_anon = count[LRU_ACTIVE_ANON] + count[LRU_INACTIVE_ANON];
        cc->nr_file = count[LRU_ACTIVE_FILE] + count[LRU_INACTIVE_FILE];
        __mod_zone_page_state(zone, NR_ISOLATED_ANON, cc->nr_anon);
        __mod_zone_page_state(zone, NR_ISOLATED_FILE, cc->nr_file);
}

/* 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;
}

/*
 * Isolate all pages that can be migrated from the block pointed to by
 * the migrate scanner within compact_control.
 */
static unsigned long isolate_migratepages(struct zone *zone,
                                        struct compact_control *cc)
{
        unsigned long low_pfn, end_pfn;
        unsigned long last_pageblock_nr = 0, pageblock_nr;
        unsigned long nr_scanned = 0, nr_isolated = 0;
        struct list_head *migratelist = &cc->migratepages;

        /* 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 0;
        }

        /*
         * 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))) {
                congestion_wait(BLK_RW_ASYNC, HZ/10);

                if (fatal_signal_pending(current))
                        return 0;
        }

        /* Time to isolate some pages for migration */
        spin_lock_irq(&zone->lru_lock);
        for (; low_pfn < end_pfn; low_pfn++) {
                struct page *page;
                if (!pfn_valid_within(low_pfn))
                        continue;
                nr_scanned++;

                /* Get the page and skip if free */
                page = pfn_to_page(low_pfn);
                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
                 */
                pageblock_nr = low_pfn >> pageblock_order;
                if (!cc->sync && last_pageblock_nr != pageblock_nr &&
                                get_pageblock_migratetype(page) != MIGRATE_MOVABLE) {
                        low_pfn += pageblock_nr_pages;
                        low_pfn = ALIGN(low_pfn, pageblock_nr_pages) - 1;
                        last_pageblock_nr = pageblock_nr;
                        continue;
                }

                if (!PageLRU(page))
                        continue;

                /*
                 * PageLRU is set, and lru_lock excludes isolation,
                 * splitting and collapsing (collapsing has already
                 * happened if PageLRU is set).
                 */
                if (PageTransHuge(page)) {
                        low_pfn += (1 << compound_order(page)) - 1;
                        continue;
                }

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

                VM_BUG_ON(PageTransCompound(page));

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

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

        acct_isolated(zone, cc);

        spin_unlock_irq(&zone->lru_lock);
        cc->migrate_pfn = low_pfn;

        trace_mm_compaction_isolate_migratepages(nr_scanned, nr_isolated);

        return cc->nr_migratepages;
}

/*
 * 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;
}

static int compact_finished(struct zone *zone,
                            struct compact_control *cc)
{
        unsigned int order;
        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)
                return COMPACT_COMPLETE;

        /* 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;

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

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

                /* Job done if allocation would set block type */
                if (order >= pageblock_order && zone->free_area[order].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;

        /*
         * 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;

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

        /*
         * fragmentation index determines if allocation failures are due to
         * low memory or external fragmentation
         *
         * index of -1 implies allocations might succeed dependingon 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 == -1 && 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;

        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 */
        cc->migrate_pfn = zone->zone_start_pfn;
        cc->free_pfn = cc->migrate_pfn + zone->spanned_pages;
        cc->free_pfn &= ~(pageblock_nr_pages-1);

        migrate_prep_local();

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

                if (!isolate_migratepages(zone, cc))
                        continue;

                nr_migrate = cc->nr_migratepages;
                err = migrate_pages(&cc->migratepages, compaction_alloc,
                                (unsigned long)cc, false,
                                cc->sync);
                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;
                }

        }

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

        return ret;
}

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

        return compact_zone(zone, &cc);
}

int sysctl_extfrag_threshold = 500;

/**
 * try_to_compact_pages - Direct compact to satisfy a high-order allocation
 * @zonelist: The zonelist used for the current allocation
 * @order: The order of the current allocation
 * @gfp_mask: The GFP mask of the current allocation
 * @nodemask: The allowed nodes to allocate from
 * @sync: Whether migration is synchronous or not
 *
 * This is the main entry point for direct page compaction.
 */
unsigned long try_to_compact_pages(struct zonelist *zonelist,
                        int order, gfp_t gfp_mask, nodemask_t *nodemask,
                        bool sync)
{
        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;

        /*
         * Check whether it is worth even starting compaction. The order check is
         * made because an assumption is made that the page allocator can satisfy
         * the "cheaper" orders without taking special steps
         */
        if (!order || !may_enter_fs || !may_perform_io)
                return rc;

        count_vm_event(COMPACTSTALL);

        /* 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);
                rc = max(status, rc);

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

        return rc;
}


/* Compact all zones within a node */
static int compact_node(int nid)
{
        int zoneid;
        pg_data_t *pgdat;
        struct zone *zone;

        if (nid < 0 || nid >= nr_node_ids || !node_online(nid))
                return -EINVAL;
        pgdat = NODE_DATA(nid);

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

        for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
                struct compact_control cc = {
                        .nr_freepages = 0,
                        .nr_migratepages = 0,
                        .order = -1,
                };

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

                cc.zone = zone;
                INIT_LIST_HEAD(&cc.freepages);
                INIT_LIST_HEAD(&cc.migratepages);

                compact_zone(zone, &cc);

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

        return 0;
}

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

        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 sys_device *dev,
                        struct sysdev_attribute *attr,
                        const char *buf, size_t count)
{
        compact_node(dev->id);

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

int compaction_register_node(struct node *node)
{
        return sysdev_create_file(&node->sysdev, &attr_compact);
}

void compaction_unregister_node(struct node *node)
{
        return sysdev_remove_file(&node->sysdev, &attr_compact);
}
#endif /* CONFIG_SYSFS && CONFIG_NUMA */