From: Bartlomiej Zolnierkiewicz <b.zolnierkie@xxxxxxxxxxx> Subject: [PATCH v7] mm: compaction: handle incorrect MIGRATE_UNMOVABLE type pageblocks When MIGRATE_UNMOVABLE pages are freed from MIGRATE_UNMOVABLE type pageblock (and some MIGRATE_MOVABLE pages are left in it) waiting until an allocation takes ownership of the block may take too long. The type of the pageblock remains unchanged so the pageblock cannot be used as a migration target during compaction. Fix it by: * Adding enum compact_mode (COMPACT_ASYNC_[MOVABLE,UNMOVABLE], and COMPACT_SYNC) and then converting sync field in struct compact_control to use it. * Adding nr_pageblocks_skipped field to struct compact_control and tracking how many destination pageblocks were of MIGRATE_UNMOVABLE type. If COMPACT_ASYNC_MOVABLE mode compaction ran fully in try_to_compact_pages() (COMPACT_COMPLETE) it implies that there is not a suitable page for allocation. In this case then check how if there were enough MIGRATE_UNMOVABLE pageblocks to try a second pass in COMPACT_ASYNC_UNMOVABLE mode. * Scanning the MIGRATE_UNMOVABLE pageblocks (during COMPACT_SYNC and COMPACT_ASYNC_UNMOVABLE compaction modes) and building a count based on finding PageBuddy pages, page_count(page) == 0 or PageLRU pages. If all pages within the MIGRATE_UNMOVABLE pageblock are in one of those three sets change the whole pageblock type to MIGRATE_MOVABLE. My particular test case (on a ARM EXYNOS4 device with 512 MiB, which means 131072 standard 4KiB pages in 'Normal' zone) is to: - allocate 120000 pages for kernel's usage - free every second page (60000 pages) of memory just allocated - allocate and use 60000 pages from user space - free remaining 60000 pages of kernel memory (now we have fragmented memory occupied mostly by user space pages) - try to allocate 100 order-9 (2048 KiB) pages for kernel's usage The results: - with compaction disabled I get 11 successful allocations - with compaction enabled - 14 successful allocations - with this patch I'm able to get all 100 successful allocations NOTE: If we can make kswapd aware of order-0 request during compaction, we can enhance kswapd with changing mode to COMPACT_ASYNC_FULL (COMPACT_ASYNC_MOVABLE + COMPACT_ASYNC_UNMOVABLE). Please see the following thread: http://marc.info/?l=linux-mm&m=133552069417068&w=2 Minor cleanups from Minchan Kim. Cc: Mel Gorman <mgorman@xxxxxxx> Cc: Minchan Kim <minchan@xxxxxxxxxx> Cc: Rik van Riel <riel@xxxxxxxxxx> Cc: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@xxxxxxxxxxx> Signed-off-by: Kyungmin Park <kyungmin.park@xxxxxxxxxxx> --- v2: - redo the patch basing on review from Mel Gorman (http://marc.info/?l=linux-mm&m=133519311025444&w=2) v3: - apply review comments from Minchan Kim (http://marc.info/?l=linux-mm&m=133531540308862&w=2) v4: - more review comments from Mel (http://marc.info/?l=linux-mm&m=133545110625042&w=2) v5: - even more comments from Mel (http://marc.info/?l=linux-mm&m=133577669023492&w=2) - fix patch description v6: (based on comments from Minchan Kim and Mel Gorman) - add note about kswapd - rename nr_pageblocks to nr_pageblocks_scanned_scanned and nr_skipped to nr_pageblocks_scanned_skipped - fix pageblocks counting in suitable_migration_target() - fix try_to_compact_pages() to do COMPACT_ASYNC_UNMOVABLE per zone v7: - minor cleanups from Minchan Kim - cleanup try_to_compact_pages() include/linux/compaction.h | 19 ++++++ mm/compaction.c | 124 +++++++++++++++++++++++++++++++++++++-------- mm/internal.h | 9 ++- mm/page_alloc.c | 8 +- 4 files changed, 134 insertions(+), 26 deletions(-) Index: b/include/linux/compaction.h =================================================================== --- a/include/linux/compaction.h 2012-05-07 11:34:50.000000000 +0200 +++ b/include/linux/compaction.h 2012-05-07 11:35:29.032707770 +0200 @@ -1,6 +1,8 @@ #ifndef _LINUX_COMPACTION_H #define _LINUX_COMPACTION_H +#include <linux/node.h> + /* Return values for compact_zone() and try_to_compact_pages() */ /* compaction didn't start as it was not possible or direct reclaim was more suitable */ #define COMPACT_SKIPPED 0 @@ -11,6 +13,23 @@ /* The full zone was compacted */ #define COMPACT_COMPLETE 3 +/* + * compaction supports three modes + * + * COMPACT_ASYNC_MOVABLE uses asynchronous migration and only scans + * MIGRATE_MOVABLE pageblocks as migration sources and targets. + * COMPACT_ASYNC_UNMOVABLE uses asynchronous migration and only scans + * MIGRATE_MOVABLE pageblocks as migration sources. + * MIGRATE_UNMOVABLE pageblocks are scanned as potential migration + * targets and convers them to MIGRATE_MOVABLE if possible + * COMPACT_SYNC uses synchronous migration and scans all pageblocks + */ +enum compact_mode { + COMPACT_ASYNC_MOVABLE, + COMPACT_ASYNC_UNMOVABLE, + COMPACT_SYNC, +}; + #ifdef CONFIG_COMPACTION extern int sysctl_compact_memory; extern int sysctl_compaction_handler(struct ctl_table *table, int write, Index: b/mm/compaction.c =================================================================== --- a/mm/compaction.c 2012-05-07 11:34:53.000000000 +0200 +++ b/mm/compaction.c 2012-05-07 11:39:06.668707335 +0200 @@ -235,7 +235,7 @@ */ while (unlikely(too_many_isolated(zone))) { /* async migration should just abort */ - if (!cc->sync) + if (cc->mode != COMPACT_SYNC) return 0; congestion_wait(BLK_RW_ASYNC, HZ/10); @@ -303,7 +303,8 @@ * satisfies the allocation */ pageblock_nr = low_pfn >> pageblock_order; - if (!cc->sync && last_pageblock_nr != pageblock_nr && + if (cc->mode != COMPACT_SYNC && + last_pageblock_nr != pageblock_nr && !migrate_async_suitable(get_pageblock_migratetype(page))) { low_pfn += pageblock_nr_pages; low_pfn = ALIGN(low_pfn, pageblock_nr_pages) - 1; @@ -324,7 +325,7 @@ continue; } - if (!cc->sync) + if (cc->mode != COMPACT_SYNC) mode |= ISOLATE_ASYNC_MIGRATE; /* Try isolate the page */ @@ -357,27 +358,82 @@ #endif /* CONFIG_COMPACTION || CONFIG_CMA */ #ifdef CONFIG_COMPACTION +static bool rescue_unmovable_pageblock(struct page *page) +{ + unsigned long pfn, start_pfn, end_pfn; + struct page *start_page, *end_page; + + pfn = page_to_pfn(page); + start_pfn = pfn & ~(pageblock_nr_pages - 1); + end_pfn = start_pfn + pageblock_nr_pages; + + start_page = pfn_to_page(start_pfn); + end_page = pfn_to_page(end_pfn); + + /* Do not deal with pageblocks that overlap zones */ + if (page_zone(start_page) != page_zone(end_page)) + return false; + + for (page = start_page, pfn = start_pfn; page < end_page; pfn++, + page++) { + if (!pfn_valid_within(pfn)) + continue; + + if (PageBuddy(page)) { + int order = page_order(page); + + pfn += (1 << order) - 1; + page += (1 << order) - 1; + + continue; + } else if (page_count(page) == 0 || PageLRU(page)) + continue; + + return false; + } + + set_pageblock_migratetype(page, MIGRATE_MOVABLE); + move_freepages_block(page_zone(page), page, MIGRATE_MOVABLE); + return true; +} + +enum result_smt { + GOOD_AS_MIGRATION_TARGET, + FAIL_UNMOVABLE, + FAIL_ETC_REASON, +}; /* Returns true if the page is within a block suitable for migration to */ -static bool suitable_migration_target(struct page *page) +static enum result_smt suitable_migration_target(struct page *page, + struct compact_control *cc) { 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; + return FAIL_ETC_REASON; /* If the page is a large free page, then allow migration */ if (PageBuddy(page) && page_order(page) >= pageblock_order) - return true; + return GOOD_AS_MIGRATION_TARGET; /* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */ - if (migrate_async_suitable(migratetype)) - return true; + if (cc->mode != COMPACT_ASYNC_UNMOVABLE && + migrate_async_suitable(migratetype)) + return GOOD_AS_MIGRATION_TARGET; + + if (cc->mode == COMPACT_ASYNC_MOVABLE && + migratetype == MIGRATE_UNMOVABLE) + return FAIL_UNMOVABLE; + + if (cc->mode != COMPACT_ASYNC_MOVABLE && + migratetype == MIGRATE_UNMOVABLE && + rescue_unmovable_pageblock(page)) + return GOOD_AS_MIGRATION_TARGET; /* Otherwise skip the block */ - return false; + return FAIL_ETC_REASON; } /* @@ -410,6 +466,8 @@ zone_end_pfn = zone->zone_start_pfn + zone->spanned_pages; + cc->nr_pageblocks_skipped = 0; + /* * Isolate free pages until enough are available to migrate the * pages on cc->migratepages. We stop searching if the migrate @@ -418,6 +476,7 @@ for (; pfn > low_pfn && cc->nr_migratepages > nr_freepages; pfn -= pageblock_nr_pages) { unsigned long isolated; + enum result_smt ret; if (!pfn_valid(pfn)) continue; @@ -434,9 +493,12 @@ continue; /* Check the block is suitable for migration */ - if (!suitable_migration_target(page)) + ret = suitable_migration_target(page, cc); + if (ret != GOOD_AS_MIGRATION_TARGET) { + if (ret == FAIL_UNMOVABLE) + cc->nr_pageblocks_skipped++; continue; - + } /* * Found a block suitable for isolating free pages from. Now * we disabled interrupts, double check things are ok and @@ -445,7 +507,8 @@ */ isolated = 0; spin_lock_irqsave(&zone->lock, flags); - if (suitable_migration_target(page)) { + ret = suitable_migration_target(page, cc); + if (ret == GOOD_AS_MIGRATION_TARGET) { end_pfn = min(pfn + pageblock_nr_pages, zone_end_pfn); isolated = isolate_freepages_block(pfn, end_pfn, freelist, false); @@ -682,8 +745,9 @@ nr_migrate = cc->nr_migratepages; err = migrate_pages(&cc->migratepages, compaction_alloc, - (unsigned long)cc, false, - cc->sync ? MIGRATE_SYNC_LIGHT : MIGRATE_ASYNC); + (unsigned long)cc, false, + (cc->mode == COMPACT_SYNC) ? MIGRATE_SYNC_LIGHT + : MIGRATE_ASYNC); update_nr_listpages(cc); nr_remaining = cc->nr_migratepages; @@ -712,7 +776,8 @@ static unsigned long compact_zone_order(struct zone *zone, int order, gfp_t gfp_mask, - bool sync) + enum compact_mode mode, + unsigned long *nr_pageblocks_skipped) { struct compact_control cc = { .nr_freepages = 0, @@ -720,12 +785,17 @@ .order = order, .migratetype = allocflags_to_migratetype(gfp_mask), .zone = zone, - .sync = sync, + .mode = mode, }; + unsigned long rc; + INIT_LIST_HEAD(&cc.freepages); INIT_LIST_HEAD(&cc.migratepages); - return compact_zone(zone, &cc); + rc = compact_zone(zone, &cc); + *nr_pageblocks_skipped = cc.nr_pageblocks_skipped; + + return rc; } int sysctl_extfrag_threshold = 500; @@ -750,6 +820,8 @@ struct zoneref *z; struct zone *zone; int rc = COMPACT_SKIPPED; + unsigned long nr_pageblocks_skipped; + enum compact_mode mode; /* * Check whether it is worth even starting compaction. The order check is @@ -766,12 +838,22 @@ nodemask) { int status; - status = compact_zone_order(zone, order, gfp_mask, sync); + mode = sync ? COMPACT_SYNC : COMPACT_ASYNC_MOVABLE; +retry: + status = compact_zone_order(zone, order, gfp_mask, mode, + &nr_pageblocks_skipped); 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; + + if (rc == COMPACT_COMPLETE && mode == COMPACT_ASYNC_MOVABLE) { + if (nr_pageblocks_skipped) { + mode = COMPACT_ASYNC_UNMOVABLE; + goto retry; + } + } } return rc; @@ -805,7 +887,7 @@ if (ok && cc->order > zone->compact_order_failed) zone->compact_order_failed = cc->order + 1; /* Currently async compaction is never deferred. */ - else if (!ok && cc->sync) + else if (!ok && cc->mode == COMPACT_SYNC) defer_compaction(zone, cc->order); } @@ -820,7 +902,7 @@ { struct compact_control cc = { .order = order, - .sync = false, + .mode = COMPACT_ASYNC_MOVABLE, }; return __compact_pgdat(pgdat, &cc); @@ -830,7 +912,7 @@ { struct compact_control cc = { .order = -1, - .sync = true, + .mode = COMPACT_SYNC, }; return __compact_pgdat(NODE_DATA(nid), &cc); Index: b/mm/internal.h =================================================================== --- a/mm/internal.h 2012-05-07 11:34:53.000000000 +0200 +++ b/mm/internal.h 2012-05-07 11:36:57.548707591 +0200 @@ -95,6 +95,9 @@ /* * in mm/page_alloc.c */ +extern void set_pageblock_migratetype(struct page *page, int migratetype); +extern int move_freepages_block(struct zone *zone, struct page *page, + int migratetype); extern void __free_pages_bootmem(struct page *page, unsigned int order); extern void prep_compound_page(struct page *page, unsigned long order); #ifdef CONFIG_MEMORY_FAILURE @@ -102,6 +105,7 @@ #endif #if defined CONFIG_COMPACTION || defined CONFIG_CMA +#include <linux/compaction.h> /* * in mm/compaction.c @@ -120,11 +124,14 @@ 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 */ + enum compact_mode mode; /* Compaction mode */ int order; /* order a direct compactor needs */ int migratetype; /* MOVABLE, RECLAIMABLE etc */ struct zone *zone; + + /* Number of UNMOVABLE destination pageblocks skipped during scan */ + unsigned long nr_pageblocks_skipped; }; unsigned long Index: b/mm/page_alloc.c =================================================================== --- a/mm/page_alloc.c 2012-05-07 11:34:54.000000000 +0200 +++ b/mm/page_alloc.c 2012-05-07 11:35:29.036707770 +0200 @@ -219,7 +219,7 @@ int page_group_by_mobility_disabled __read_mostly; -static void set_pageblock_migratetype(struct page *page, int migratetype) +void set_pageblock_migratetype(struct page *page, int migratetype) { if (unlikely(page_group_by_mobility_disabled)) @@ -959,8 +959,8 @@ return pages_moved; } -static int move_freepages_block(struct zone *zone, struct page *page, - int migratetype) +int move_freepages_block(struct zone *zone, struct page *page, + int migratetype) { unsigned long start_pfn, end_pfn; struct page *start_page, *end_page; @@ -5661,7 +5661,7 @@ .nr_migratepages = 0, .order = -1, .zone = page_zone(pfn_to_page(start)), - .sync = true, + .mode = COMPACT_SYNC, }; INIT_LIST_HEAD(&cc.migratepages); -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. 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