From a34753d275576896b06af9baa6f54bee258368c2 Mon Sep 17 00:00:00 2001 From: Vlastimil Babka Date: Thu, 19 May 2016 17:11:51 -0700 Subject: mm, compaction: reduce spurious pcplist drains Compaction drains the local pcplists each time migration scanner moves away from a cc->order aligned block where it isolated pages for migration, so that the pages freed by migrations can merge into higher orders. The detection is currently coarser than it could be. The cc->last_migrated_pfn variable should track the lowest pfn that was isolated for migration. But it is set to the pfn where isolate_migratepages_block() starts scanning, which is typically the first pfn of the pageblock. There, the scanner might fail to isolate several order-aligned blocks, and then isolate COMPACT_CLUSTER_MAX in another block. This would cause the pcplists drain to be performed, although the scanner didn't yet finish the block where it isolated from. This patch thus makes cc->last_migrated_pfn handling more accurate by setting it to the pfn of an actually isolated page in isolate_migratepages_block(). Although practical effects of this patch are likely low, it arguably makes the intent of the code more obvious. Also the next patch will make async direct compaction skip blocks more aggressively, and draining pcplists due to skipped blocks is wasteful. Signed-off-by: Vlastimil Babka Cc: Joonsoo Kim Cc: Mel Gorman Cc: Rik van Riel Cc: David Rientjes Cc: Minchan Kim Cc: Michal Hocko Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/compaction.c | 20 +++++++++----------- 1 file changed, 9 insertions(+), 11 deletions(-) (limited to 'mm') diff --git a/mm/compaction.c b/mm/compaction.c index 017a1a1963cb..329973a1ae45 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -787,6 +787,15 @@ isolate_success: cc->nr_migratepages++; nr_isolated++; + /* + * Record where we could have freed pages by migration and not + * yet flushed them to buddy allocator. + * - this is the lowest page that was isolated and likely be + * then freed by migration. + */ + if (!cc->last_migrated_pfn) + cc->last_migrated_pfn = low_pfn; + /* Avoid isolating too much */ if (cc->nr_migratepages == COMPACT_CLUSTER_MAX) { ++low_pfn; @@ -1075,7 +1084,6 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone, unsigned long block_start_pfn; unsigned long block_end_pfn; unsigned long low_pfn; - unsigned long isolate_start_pfn; struct page *page; const isolate_mode_t isolate_mode = (sysctl_compact_unevictable_allowed ? ISOLATE_UNEVICTABLE : 0) | @@ -1130,7 +1138,6 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone, continue; /* Perform the isolation */ - isolate_start_pfn = low_pfn; low_pfn = isolate_migratepages_block(cc, low_pfn, block_end_pfn, isolate_mode); @@ -1139,15 +1146,6 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone, return ISOLATE_ABORT; } - /* - * Record where we could have freed pages by migration and not - * yet flushed them to buddy allocator. - * - this is the lowest page that could have been isolated and - * then freed by migration. - */ - if (cc->nr_migratepages && !cc->last_migrated_pfn) - cc->last_migrated_pfn = isolate_start_pfn; - /* * Either we isolated something and proceed with migration. Or * we failed and compact_zone should decide if we should -- cgit v1.2.3