path: root/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 <linux/balloon_compaction.h>
#include <linux/page-isolation.h>
#include "internal.h"

#ifdef CONFIG_COMPACTION
static inline void count_compact_event(enum vm_event_item item)
{
	count_vm_event(item);
}

static inline void count_compact_events(enum vm_event_item item, long delta)
{
	count_vm_events(item, delta);
}
#else
#define count_compact_event(item) do { } while (0)
#define count_compact_events(item, delta) do { } while (0)
#endif

#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 high_pfn = 0;

	list_for_each_entry_safe(page, next, freelist, lru) {
		unsigned long pfn = page_to_pfn(page);
		list_del(&page->lru);
		__free_page(page);
		if (pfn > high_pfn)
			high_pfn = pfn;
	}

	return high_pfn;
}

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;
}

/*
 * Check that the whole (or subset of) a pageblock given by the interval of
 * [start_pfn, end_pfn) is valid and within the same zone, before scanning it
 * with the migration of free compaction scanner. The scanners then need to
 * use only pfn_valid_within() check for arches that allow holes within
 * pageblocks.
 *
 * Return struct page pointer of start_pfn, or NULL if checks were not passed.
 *
 * 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. We assume that a border between node0 and node1
 * can occur within a single pageblock, but not a node0 node1 node0
 * interleaving within a single pageblock. It is therefore sufficient to check
 * the first and last page of a pageblock and avoid checking each individual
 * page in a pageblock.
 */
static struct page *pageblock_pfn_to_page(unsigned long start_pfn,
				unsigned long end_pfn, struct zone *zone)
{
	struct page *start_page;
	struct page *end_page;

	/* end_pfn is one past the range we are checking */
	end_pfn--;

	if (!pfn_valid(start_pfn) || !pfn_valid(end_pfn))
		return NULL;

	start_page = pfn_to_page(start_pfn);

	if (page_zone(start_page) != zone)
		return NULL;

	end_page = pfn_to_page(end_pfn);

	/* This gives a shorter code than deriving page_zone(end_page) */
	if (page_zone_id(start_page) != page_zone_id(end_page))
		return NULL;

	return start_page;
}

#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_end_pfn(zone);
	unsigned long pfn;

	zone->compact_cached_migrate_pfn[0] = start_pfn;
	zone->compact_cached_migrate_pfn[1] = 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;
	unsigned long pfn;

	if (cc->ignore_skip_hint)
		return;

	if (!page)
		return;

	if (nr_isolated)
		return;

	set_pageblock_skip(page);

	pfn = page_to_pfn(page);

	/* Update where async and sync compaction should restart */
	if (migrate_scanner) {
		if (pfn > zone->compact_cached_migrate_pfn[0])
			zone->compact_cached_migrate_pfn[0] = pfn;
		if (cc->mode != MIGRATE_ASYNC &&
		    pfn > zone->compact_cached_migrate_pfn[1])
			zone->compact_cached_migrate_pfn[1] = pfn;
	} else {
		if (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 */

/*
 * Compaction requires the taking of some coarse locks that are potentially
 * very heavily contended. For async compaction, back out if the lock cannot
 * be taken immediately. For sync compaction, spin on the lock if needed.
 *
 * Returns true if the lock is held
 * Returns false if the lock is not held and compaction should abort
 */
static bool compact_trylock_irqsave(spinlock_t *lock, unsigned long *flags