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 "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