From 539aa041a9b1d98cd847b949ba8f91857c995f26 Mon Sep 17 00:00:00 2001 From: Mel Gorman Date: Mon, 15 May 2023 12:33:41 +0100 Subject: [PATCH] mm: compaction: ensure rescanning only happens on partially scanned pageblocks Patch series "Follow-up "Fix excessive CPU usage during compaction"". The series "Fix excessive CPU usage during compaction" [1] attempted to fix a bug [2] but Vlastimil noted that the fix was incomplete [3]. While the series was merged, fast_find_migrateblock was still disabled. This series should fix the corner cases and allow 95e7a450b819 ("Revert "mm/compaction: fix set skip in fast_find_migrateblock"") to be safely reverted. Details on how many pageblocks are rescanned are in the changelog of the last patch. "Raghavendra K T" tested this and reported "decent improvement from perf perspective as well as compaction related data [4] [1] https://lore.kernel.org/r/20230125134434.18017-1-mgorman@techsingularity.net [2] https://bugzilla.suse.com/show_bug.cgi?id=1206848 [3] https://lore.kernel.org/r/a55cf026-a2f9-ef01-9a4c-398693e048ea@suse.cz [4] https://lkml.kernel.org/r/6d62686f-964d-342c-e085-0eae2555cc54@amd.com This patch (of 4): compact_zone() intends to rescan pageblocks if there is a failure to migrate "within the current order-aligned block". However, the pageblock scan may already be complete and moved to the next block causing the next pageblock to be "rescanned". Ensure only the most recent pageblock is rescanned. Link: https://lkml.kernel.org/r/20230515113344.6869-1-mgorman@techsingularity.net Link: https://lkml.kernel.org/r/20230515113344.6869-2-mgorman@techsingularity.net Signed-off-by: Mel Gorman Reported-by: Vlastimil Babka Tested-by: Raghavendra K T Acked-by: Vlastimil Babka Cc: Chuyi Zhou Cc: Jiri Slaby Cc: Maxim Levitsky Cc: Mel Gorman Cc: Michal Hocko Cc: Paolo Bonzini Cc: Pedro Falcato Signed-off-by: Andrew Morton --- mm/compaction.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/mm/compaction.c b/mm/compaction.c index 5584fa5fa3d4..d16b0fcd6db5 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -2465,8 +2465,9 @@ rescan: * fast_find_migrateblock revisiting blocks that were * recently partially scanned. */ - if (cc->direct_compaction && !cc->finish_pageblock && - (cc->mode < MIGRATE_SYNC)) { + if (!pageblock_aligned(cc->migrate_pfn) && + cc->direct_compaction && !cc->finish_pageblock && + (cc->mode < MIGRATE_SYNC)) { cc->finish_pageblock = true; /*