linux-kernel - [PATCH 2/4] mm: compaction: Only force pageblock scan completion when skip hints are obeyed

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Message-Id: <20230515113344.6869-3-mgorman@techsingularity.net>
Date:   Mon, 15 May 2023 12:33:42 +0100
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        Michal Hocko <mhocko@...nel.org>,
        Pedro Falcato <pedro.falcato@...il.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Chuyi Zhou <zhouchuyi@...edance.com>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Mel Gorman <mgorman@...hsingularity.net>
Subject: [PATCH 2/4] mm: compaction: Only force pageblock scan completion when skip hints are obeyed

fast_find_migrateblock relies on skip hints to avoid rescanning a recently
selected pageblock but compact_zone() only forces the pageblock scan
completion to set the skip hint if in direct compaction.  While this
prevents direct compaction repeatedly scanning a subset of blocks due
to fast_find_migrateblock(), it does not prevent proactive compaction,
node compaction and kcompactd encountering the same problem described
in commit cfccd2e63e7e ("mm, compaction: finish pageblocks on complete
migration failure").

Force the scan completion of a pageblock to set the skip hint if skip
hints are obeyed to prevent fast_find_migrateblock() repeatedly selecting
a subset of pageblocks.

Suggested-by: Vlastimil Babka <vbabka@...e.cz>
Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>
---
 mm/compaction.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index 81791c124bb8..accc6568091a 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -2456,7 +2456,8 @@ compact_zone(struct compact_control *cc, struct capture_control *capc)
 			}
 			/*
 			 * If an ASYNC or SYNC_LIGHT fails to migrate a page
-			 * within the current order-aligned block, scan the
+			 * within the current order-aligned block and
+			 * fast_find_migrateblock may be used then scan the
 			 * remainder of the pageblock. This will mark the
 			 * pageblock "skip" to avoid rescanning in the near
 			 * future. This will isolate more pages than necessary
@@ -2465,7 +2466,7 @@ compact_zone(struct compact_control *cc, struct capture_control *capc)
 			 * recently partially scanned.
 			 */
 			if (!pageblock_aligned(cc->migrate_pfn) &&
-			    cc->direct_compaction && !cc->finish_pageblock &&
+			    !cc->ignore_skip_hint && !cc->finish_pageblock &&
 			    (cc->mode < MIGRATE_SYNC)) {
 				cc->finish_pageblock = true;
 
-- 
2.35.3