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 <mgorman@techsingularity.net>
Reported-by: Vlastimil Babka <vbabka@suse.cz>
Tested-by: Raghavendra K T <raghavendra.kt@amd.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Chuyi Zhou <zhouchuyi@bytedance.com>
Cc: Jiri Slaby <jirislaby@kernel.org>
Cc: Maxim Levitsky <mlevitsk@redhat.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Pedro Falcato <pedro.falcato@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/compaction.c b/mm/compaction.c
index 5584fa5fa3d4dc5427833193ab04a7957eca7dac..d16b0fcd6db5a3c94e0b963bad221cf468381e9c 100644 (file)
--- 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;
 
                                /*