blob: be1ff3f7552bf069195f2ff520f276121d139210 [file] [log] [blame]
/*
* 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 "internal.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 */
/* Account for isolated anon and file pages */
unsigned long nr_anon;
unsigned long nr_file;
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 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;
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;
}
}
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.
*/
spin_lock_irqsave(&zone->lock, flags);
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 */
isolated = isolate_freepages_block(zone, pfn, freelist);
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)
high_pfn = max(high_pfn, pfn);
}
spin_unlock_irqrestore(&zone->lock, flags);
/* 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 inactive, isolated;
inactive = zone_page_state(zone, NR_INACTIVE_FILE) +
zone_page_state(zone, NR_INACTIVE_ANON);
isolated = zone_page_state(zone, NR_ISOLATED_FILE) +
zone_page_state(zone, NR_ISOLATED_ANON);
return isolated > inactive;
}
/*
* 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;
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;
/* Get the page and skip if free */
page = pfn_to_page(low_pfn);
if (PageBuddy(page))
continue;
/* Try isolate the page */
if (__isolate_lru_page(page, ISOLATE_BOTH, 0) != 0)
continue;
/* Successfully isolated */
del_page_from_lru_list(zone, page, page_lru(page));
list_add(&page->lru, migratelist);
mem_cgroup_del_lru(page);
cc->nr_migratepages++;
/* 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;
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)
{
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;
return COMPACT_CONTINUE;
}
static int compact_zone(struct zone *zone, struct compact_control *cc)
{
int ret;
/* 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;
if (!isolate_migratepages(zone, cc))
continue;
nr_migrate = cc->nr_migratepages;
migrate_pages(&cc->migratepages, compaction_alloc,
(unsigned long)cc, 0);
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);
/* Release LRU pages not migrated */
if (!list_empty(&cc->migratepages)) {
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;
}