+ mm-compaction-update-pageblock-skip-when-first-migration-candidate-is-not-at-the-start-fix.patch added to mm-unstable branch

+ mm-compaction-update-pageblock-skip-when-first-migration-candidate-is-not-at-the-start-fix.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm-compaction-update-pageblock-skip-when-first-migration-candidate-is-not-at-the-start-fix
has been added to the -mm mm-unstable branch.  Its filename is
     mm-compaction-update-pageblock-skip-when-first-migration-candidate-is-not-at-the-start-fix.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-compaction-update-pageblock-skip-when-first-migration-candidate-is-not-at-the-start-fix.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Mel Gorman <mgorman@techsingularity.net>
Subject: mm-compaction-update-pageblock-skip-when-first-migration-candidate-is-not-at-the-start-fix
Date: Fri, 2 Jun 2023 12:16:22 +0100

Vlastimil Babka pointed out the following problem with
mm-compaction-update-pageblock-skip-when-first-migration-candidate-is-not-at-the-start.patch

	I wonder if this has an unintended side-effect that if we resume
	isolate_migratepages_block() of a partially compacted pageblock
	to finish it, test_and_set_skip() will now tell us to abort,
	because we already set the skip bit in the previous call. This
	would include the cc->finish_pageblock rescan cases.

He is correct and a partial rescan as implemented in "mm, compaction:
finish pageblocks on complete migration failure" would abort prematurely.

Test and set the skip bit when acquiring "exclusive access" to a pageblock
for migration but only abort if the calling context is not rescanning to
finish a pageblock.

This is a fix for the mmotm patch
mm-compaction-update-pageblock-skip-when-first-migration-candidate-is-not-at-the-start.patch

Link: https://lkml.kernel.org/r/20230602111622.swtxhn6lu2qwgrwq@techsingularity.net
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
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: Michal Hocko <mhocko@kernel.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Pedro Falcato <pedro.falcato@gmail.com>
Cc: Raghavendra K T <raghavendra.kt@amd.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/compaction.c |   10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

--- a/mm/compaction.c~mm-compaction-update-pageblock-skip-when-first-migration-candidate-is-not-at-the-start-fix
+++ a/mm/compaction.c
@@ -1069,11 +1069,17 @@ isolate_migratepages_block(struct compac
 
 			lruvec_memcg_debug(lruvec, page_folio(page));
 
-			/* Try get exclusive access under lock */
+			/*
+			 * Try get exclusive access under lock. If marked for
+			 * skip, the scan is aborted unless the current context
+			 * is a rescan to reach the end of the pageblock.
+			 */
 			if (!skip_updated && valid_page) {
 				skip_updated = true;
-				if (test_and_set_skip(cc, valid_page))
+				if (test_and_set_skip(cc, valid_page) &&
+				    !cc->finish_pageblock) {
 					goto isolate_abort;
+				}
 			}
 
 			/*
_

Patches currently in -mm which might be from mgorman@techsingularity.net are

mm-compaction-ensure-rescanning-only-happens-on-partially-scanned-pageblocks.patch
mm-compaction-only-force-pageblock-scan-completion-when-skip-hints-are-obeyed.patch
mm-compaction-update-pageblock-skip-when-first-migration-candidate-is-not-at-the-start.patch
mm-compaction-update-pageblock-skip-when-first-migration-candidate-is-not-at-the-start-fix.patch
revert-revert-mm-compaction-fix-set-skip-in-fast_find_migrateblock.patch