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![Johannes Weiner](/assets/img/avatar_default.png)
Up until 3e7d344
("mm: vmscan: reclaim order-0 and use compaction instead
of lumpy reclaim"), compaction skipped calculating the fragmentation index
of a zone when compaction was explicitely requested through the procfs
knob.
However, when compaction_suitable was introduced, it did not come with an
extra check for order == -1, set on explicit compaction requests, and
passed this order on to the fragmentation index calculation, where it
overshifts the number of requested pages, leading to a division by zero.
This patch makes sure that order == -1 is recognized as the flag it is
rather than passing it along as valid order parameter.
[akpm@linux-foundation.org: add comment, per Mel]
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
706 lines
19 KiB
C
706 lines
19 KiB
C
/*
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* linux/mm/compaction.c
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*
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* Memory compaction for the reduction of external fragmentation. Note that
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* this heavily depends upon page migration to do all the real heavy
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* lifting
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*
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* Copyright IBM Corp. 2007-2010 Mel Gorman <mel@csn.ul.ie>
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*/
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#include <linux/swap.h>
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#include <linux/migrate.h>
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#include <linux/compaction.h>
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#include <linux/mm_inline.h>
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#include <linux/backing-dev.h>
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#include <linux/sysctl.h>
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#include <linux/sysfs.h>
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#include "internal.h"
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#define CREATE_TRACE_POINTS
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#include <trace/events/compaction.h>
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/*
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* compact_control is used to track pages being migrated and the free pages
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* they are being migrated to during memory compaction. The free_pfn starts
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* at the end of a zone and migrate_pfn begins at the start. Movable pages
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* are moved to the end of a zone during a compaction run and the run
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* completes when free_pfn <= migrate_pfn
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*/
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struct compact_control {
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struct list_head freepages; /* List of free pages to migrate to */
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struct list_head migratepages; /* List of pages being migrated */
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unsigned long nr_freepages; /* Number of isolated free pages */
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unsigned long nr_migratepages; /* Number of pages to migrate */
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unsigned long free_pfn; /* isolate_freepages search base */
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unsigned long migrate_pfn; /* isolate_migratepages search base */
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bool sync; /* Synchronous migration */
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/* Account for isolated anon and file pages */
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unsigned long nr_anon;
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unsigned long nr_file;
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unsigned int order; /* order a direct compactor needs */
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int migratetype; /* MOVABLE, RECLAIMABLE etc */
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struct zone *zone;
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int compact_mode;
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};
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static unsigned long release_freepages(struct list_head *freelist)
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{
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struct page *page, *next;
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unsigned long count = 0;
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list_for_each_entry_safe(page, next, freelist, lru) {
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list_del(&page->lru);
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__free_page(page);
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count++;
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}
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return count;
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}
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/* Isolate free pages onto a private freelist. Must hold zone->lock */
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static unsigned long isolate_freepages_block(struct zone *zone,
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unsigned long blockpfn,
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struct list_head *freelist)
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{
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unsigned long zone_end_pfn, end_pfn;
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int nr_scanned = 0, total_isolated = 0;
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struct page *cursor;
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/* Get the last PFN we should scan for free pages at */
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zone_end_pfn = zone->zone_start_pfn + zone->spanned_pages;
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end_pfn = min(blockpfn + pageblock_nr_pages, zone_end_pfn);
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/* Find the first usable PFN in the block to initialse page cursor */
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for (; blockpfn < end_pfn; blockpfn++) {
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if (pfn_valid_within(blockpfn))
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break;
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}
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cursor = pfn_to_page(blockpfn);
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/* Isolate free pages. This assumes the block is valid */
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for (; blockpfn < end_pfn; blockpfn++, cursor++) {
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int isolated, i;
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struct page *page = cursor;
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if (!pfn_valid_within(blockpfn))
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continue;
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nr_scanned++;
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if (!PageBuddy(page))
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continue;
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/* Found a free page, break it into order-0 pages */
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isolated = split_free_page(page);
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total_isolated += isolated;
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for (i = 0; i < isolated; i++) {
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list_add(&page->lru, freelist);
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page++;
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}
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/* If a page was split, advance to the end of it */
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if (isolated) {
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blockpfn += isolated - 1;
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cursor += isolated - 1;
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}
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}
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trace_mm_compaction_isolate_freepages(nr_scanned, total_isolated);
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return total_isolated;
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}
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/* Returns true if the page is within a block suitable for migration to */
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static bool suitable_migration_target(struct page *page)
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{
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int migratetype = get_pageblock_migratetype(page);
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/* Don't interfere with memory hot-remove or the min_free_kbytes blocks */
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if (migratetype == MIGRATE_ISOLATE || migratetype == MIGRATE_RESERVE)
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return false;
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/* If the page is a large free page, then allow migration */
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if (PageBuddy(page) && page_order(page) >= pageblock_order)
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return true;
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/* If the block is MIGRATE_MOVABLE, allow migration */
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if (migratetype == MIGRATE_MOVABLE)
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return true;
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/* Otherwise skip the block */
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return false;
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}
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/*
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* Based on information in the current compact_control, find blocks
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* suitable for isolating free pages from and then isolate them.
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*/
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static void isolate_freepages(struct zone *zone,
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struct compact_control *cc)
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{
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struct page *page;
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unsigned long high_pfn, low_pfn, pfn;
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unsigned long flags;
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int nr_freepages = cc->nr_freepages;
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struct list_head *freelist = &cc->freepages;
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pfn = cc->free_pfn;
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low_pfn = cc->migrate_pfn + pageblock_nr_pages;
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high_pfn = low_pfn;
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/*
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* Isolate free pages until enough are available to migrate the
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* pages on cc->migratepages. We stop searching if the migrate
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* and free page scanners meet or enough free pages are isolated.
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*/
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spin_lock_irqsave(&zone->lock, flags);
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for (; pfn > low_pfn && cc->nr_migratepages > nr_freepages;
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pfn -= pageblock_nr_pages) {
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unsigned long isolated;
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if (!pfn_valid(pfn))
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continue;
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/*
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* Check for overlapping nodes/zones. It's possible on some
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* configurations to have a setup like
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* node0 node1 node0
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* i.e. it's possible that all pages within a zones range of
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* pages do not belong to a single zone.
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*/
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page = pfn_to_page(pfn);
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if (page_zone(page) != zone)
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continue;
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/* Check the block is suitable for migration */
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if (!suitable_migration_target(page))
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continue;
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/* Found a block suitable for isolating free pages from */
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isolated = isolate_freepages_block(zone, pfn, freelist);
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nr_freepages += isolated;
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/*
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* Record the highest PFN we isolated pages from. When next
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* looking for free pages, the search will restart here as
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* page migration may have returned some pages to the allocator
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*/
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if (isolated)
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high_pfn = max(high_pfn, pfn);
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}
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spin_unlock_irqrestore(&zone->lock, flags);
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/* split_free_page does not map the pages */
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list_for_each_entry(page, freelist, lru) {
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arch_alloc_page(page, 0);
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kernel_map_pages(page, 1, 1);
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}
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cc->free_pfn = high_pfn;
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cc->nr_freepages = nr_freepages;
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}
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/* Update the number of anon and file isolated pages in the zone */
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static void acct_isolated(struct zone *zone, struct compact_control *cc)
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{
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struct page *page;
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unsigned int count[NR_LRU_LISTS] = { 0, };
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list_for_each_entry(page, &cc->migratepages, lru) {
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int lru = page_lru_base_type(page);
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count[lru]++;
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}
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cc->nr_anon = count[LRU_ACTIVE_ANON] + count[LRU_INACTIVE_ANON];
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cc->nr_file = count[LRU_ACTIVE_FILE] + count[LRU_INACTIVE_FILE];
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__mod_zone_page_state(zone, NR_ISOLATED_ANON, cc->nr_anon);
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__mod_zone_page_state(zone, NR_ISOLATED_FILE, cc->nr_file);
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}
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/* Similar to reclaim, but different enough that they don't share logic */
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static bool too_many_isolated(struct zone *zone)
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{
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unsigned long active, inactive, isolated;
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inactive = zone_page_state(zone, NR_INACTIVE_FILE) +
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zone_page_state(zone, NR_INACTIVE_ANON);
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active = zone_page_state(zone, NR_ACTIVE_FILE) +
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zone_page_state(zone, NR_ACTIVE_ANON);
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isolated = zone_page_state(zone, NR_ISOLATED_FILE) +
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zone_page_state(zone, NR_ISOLATED_ANON);
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return isolated > (inactive + active) / 2;
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}
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/*
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* Isolate all pages that can be migrated from the block pointed to by
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* the migrate scanner within compact_control.
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*/
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static unsigned long isolate_migratepages(struct zone *zone,
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struct compact_control *cc)
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{
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unsigned long low_pfn, end_pfn;
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unsigned long last_pageblock_nr = 0, pageblock_nr;
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unsigned long nr_scanned = 0, nr_isolated = 0;
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struct list_head *migratelist = &cc->migratepages;
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/* Do not scan outside zone boundaries */
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low_pfn = max(cc->migrate_pfn, zone->zone_start_pfn);
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/* Only scan within a pageblock boundary */
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end_pfn = ALIGN(low_pfn + pageblock_nr_pages, pageblock_nr_pages);
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/* Do not cross the free scanner or scan within a memory hole */
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if (end_pfn > cc->free_pfn || !pfn_valid(low_pfn)) {
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cc->migrate_pfn = end_pfn;
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return 0;
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}
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/*
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* Ensure that there are not too many pages isolated from the LRU
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* list by either parallel reclaimers or compaction. If there are,
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* delay for some time until fewer pages are isolated
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*/
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while (unlikely(too_many_isolated(zone))) {
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congestion_wait(BLK_RW_ASYNC, HZ/10);
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if (fatal_signal_pending(current))
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return 0;
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}
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/* Time to isolate some pages for migration */
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spin_lock_irq(&zone->lru_lock);
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for (; low_pfn < end_pfn; low_pfn++) {
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struct page *page;
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if (!pfn_valid_within(low_pfn))
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continue;
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nr_scanned++;
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/* Get the page and skip if free */
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page = pfn_to_page(low_pfn);
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if (PageBuddy(page))
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continue;
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/*
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* For async migration, also only scan in MOVABLE blocks. Async
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* migration is optimistic to see if the minimum amount of work
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* satisfies the allocation
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*/
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pageblock_nr = low_pfn >> pageblock_order;
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if (!cc->sync && last_pageblock_nr != pageblock_nr &&
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get_pageblock_migratetype(page) != MIGRATE_MOVABLE) {
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low_pfn += pageblock_nr_pages;
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low_pfn = ALIGN(low_pfn, pageblock_nr_pages) - 1;
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last_pageblock_nr = pageblock_nr;
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continue;
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}
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if (!PageLRU(page))
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continue;
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/*
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* PageLRU is set, and lru_lock excludes isolation,
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* splitting and collapsing (collapsing has already
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* happened if PageLRU is set).
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*/
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if (PageTransHuge(page)) {
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low_pfn += (1 << compound_order(page)) - 1;
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continue;
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}
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/* Try isolate the page */
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if (__isolate_lru_page(page, ISOLATE_BOTH, 0) != 0)
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continue;
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VM_BUG_ON(PageTransCompound(page));
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/* Successfully isolated */
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del_page_from_lru_list(zone, page, page_lru(page));
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list_add(&page->lru, migratelist);
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cc->nr_migratepages++;
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nr_isolated++;
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/* Avoid isolating too much */
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if (cc->nr_migratepages == COMPACT_CLUSTER_MAX)
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break;
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}
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acct_isolated(zone, cc);
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spin_unlock_irq(&zone->lru_lock);
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cc->migrate_pfn = low_pfn;
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trace_mm_compaction_isolate_migratepages(nr_scanned, nr_isolated);
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return cc->nr_migratepages;
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}
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/*
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* This is a migrate-callback that "allocates" freepages by taking pages
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* from the isolated freelists in the block we are migrating to.
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*/
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static struct page *compaction_alloc(struct page *migratepage,
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unsigned long data,
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int **result)
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{
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struct compact_control *cc = (struct compact_control *)data;
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struct page *freepage;
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/* Isolate free pages if necessary */
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if (list_empty(&cc->freepages)) {
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isolate_freepages(cc->zone, cc);
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if (list_empty(&cc->freepages))
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return NULL;
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}
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freepage = list_entry(cc->freepages.next, struct page, lru);
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list_del(&freepage->lru);
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cc->nr_freepages--;
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return freepage;
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}
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/*
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* We cannot control nr_migratepages and nr_freepages fully when migration is
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* running as migrate_pages() has no knowledge of compact_control. When
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* migration is complete, we count the number of pages on the lists by hand.
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*/
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static void update_nr_listpages(struct compact_control *cc)
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{
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int nr_migratepages = 0;
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int nr_freepages = 0;
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struct page *page;
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list_for_each_entry(page, &cc->migratepages, lru)
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nr_migratepages++;
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list_for_each_entry(page, &cc->freepages, lru)
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nr_freepages++;
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cc->nr_migratepages = nr_migratepages;
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cc->nr_freepages = nr_freepages;
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}
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static int compact_finished(struct zone *zone,
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struct compact_control *cc)
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{
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unsigned int order;
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unsigned long watermark;
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if (fatal_signal_pending(current))
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return COMPACT_PARTIAL;
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/* Compaction run completes if the migrate and free scanner meet */
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if (cc->free_pfn <= cc->migrate_pfn)
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return COMPACT_COMPLETE;
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/* Compaction run is not finished if the watermark is not met */
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if (cc->compact_mode != COMPACT_MODE_KSWAPD)
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watermark = low_wmark_pages(zone);
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else
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watermark = high_wmark_pages(zone);
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watermark += (1 << cc->order);
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if (!zone_watermark_ok(zone, cc->order, watermark, 0, 0))
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return COMPACT_CONTINUE;
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/*
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* order == -1 is expected when compacting via
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* /proc/sys/vm/compact_memory
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*/
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if (cc->order == -1)
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return COMPACT_CONTINUE;
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/*
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* Generating only one page of the right order is not enough
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* for kswapd, we must continue until we're above the high
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* watermark as a pool for high order GFP_ATOMIC allocations
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* too.
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*/
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if (cc->compact_mode == COMPACT_MODE_KSWAPD)
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return COMPACT_CONTINUE;
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/* Direct compactor: Is a suitable page free? */
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for (order = cc->order; order < MAX_ORDER; order++) {
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/* Job done if page is free of the right migratetype */
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if (!list_empty(&zone->free_area[order].free_list[cc->migratetype]))
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return COMPACT_PARTIAL;
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/* Job done if allocation would set block type */
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if (order >= pageblock_order && zone->free_area[order].nr_free)
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return COMPACT_PARTIAL;
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}
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return COMPACT_CONTINUE;
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}
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/*
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* compaction_suitable: Is this suitable to run compaction on this zone now?
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* Returns
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* COMPACT_SKIPPED - If there are too few free pages for compaction
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* COMPACT_PARTIAL - If the allocation would succeed without compaction
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* COMPACT_CONTINUE - If compaction should run now
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*/
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unsigned long compaction_suitable(struct zone *zone, int order)
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{
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int fragindex;
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unsigned long watermark;
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/*
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* Watermarks for order-0 must be met for compaction. Note the 2UL.
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* This is because during migration, copies of pages need to be
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* allocated and for a short time, the footprint is higher
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*/
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watermark = low_wmark_pages(zone) + (2UL << order);
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if (!zone_watermark_ok(zone, 0, watermark, 0, 0))
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return COMPACT_SKIPPED;
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/*
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* order == -1 is expected when compacting via
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* /proc/sys/vm/compact_memory
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*/
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if (order == -1)
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return COMPACT_CONTINUE;
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/*
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* fragmentation index determines if allocation failures are due to
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* low memory or external fragmentation
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*
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* index of -1 implies allocations might succeed dependingon watermarks
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* index towards 0 implies failure is due to lack of memory
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* index towards 1000 implies failure is due to fragmentation
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*
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* Only compact if a failure would be due to fragmentation.
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*/
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fragindex = fragmentation_index(zone, order);
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if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold)
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return COMPACT_SKIPPED;
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if (fragindex == -1 && zone_watermark_ok(zone, order, watermark, 0, 0))
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return COMPACT_PARTIAL;
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return COMPACT_CONTINUE;
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}
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static int compact_zone(struct zone *zone, struct compact_control *cc)
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{
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int ret;
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ret = compaction_suitable(zone, cc->order);
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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;
|
|
|
|
if (!isolate_migratepages(zone, cc))
|
|
continue;
|
|
|
|
nr_migrate = cc->nr_migratepages;
|
|
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 (!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;
|
|
}
|
|
|
|
unsigned long compact_zone_order(struct zone *zone,
|
|
int order, gfp_t gfp_mask,
|
|
bool sync,
|
|
int compact_mode)
|
|
{
|
|
struct compact_control cc = {
|
|
.nr_freepages = 0,
|
|
.nr_migratepages = 0,
|
|
.order = order,
|
|
.migratetype = allocflags_to_migratetype(gfp_mask),
|
|
.zone = zone,
|
|
.sync = sync,
|
|
.compact_mode = compact_mode,
|
|
};
|
|
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,
|
|
COMPACT_MODE_DIRECT_RECLAIM);
|
|
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,
|
|
.compact_mode = COMPACT_MODE_DIRECT_RECLAIM,
|
|
};
|
|
|
|
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 */
|