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From: Andrew Morton <>
Subject: + revert-mm-compaction-fix-set-skip-in-fast_find_migrateblock.patch added to mm-hotfixes-unstable branch
Date: Fri, 13 Jan 2023 20:11:17 -0800	[thread overview]
Message-ID: <> (raw)

The patch titled
     Subject: Revert "mm/compaction: fix set skip in fast_find_migrateblock"
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is

This patch will shortly appear at

This patch will later appear in the mm-hotfixes-unstable branch at

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From: Vlastimil Babka <>
Subject: Revert "mm/compaction: fix set skip in fast_find_migrateblock"
Date: Fri, 13 Jan 2023 18:33:45 +0100

This reverts commit 7efc3b7261030da79001c00d92bc3392fd6c664c.

We have got openSUSE reports (Link 1) for 6.1 kernel with khugepaged
stalling CPU for long periods of time.  Investigation of tracepoint data
shows that compaction is stuck in repeating fast_find_migrateblock() based
migrate page isolation, and then fails to migrate all isolated pages. 
Commit 7efc3b726103 ("mm/compaction: fix set skip in
fast_find_migrateblock") was suspected as it was merged in 6.1 and in
theory can indeed remove a termination condition for
fast_find_migrateblock() under certain conditions, as it removes a place
that always marks a scanned pageblock from being re-scanned.  There are
other such places, but those can be skipped under certain conditions,
which seems to match the tracepoint data.

Testing of revert also appears to have resolved the issue, thus revert the
commit until a more robust solution for the original problem is developed.

It's also likely this will fix qemu stalls with 6.1 kernel reported in
Link 2, but that is not yet confirmed.

Fixes: 7efc3b726103 ("mm/compaction: fix set skip in fast_find_migrateblock")
Cc: Chuyi Zhou <>
Cc: Jiri Slaby <>
Cc: Maxim Levitsky <>
Cc: Mel Gorman <>
Cc: Michal Hocko <>
Cc: Paolo Bonzini <>
Cc: Thorsten Leemhuis <>
Cc: <>
Signed-off-by: Andrew Morton <>

--- a/mm/compaction.c~revert-mm-compaction-fix-set-skip-in-fast_find_migrateblock
+++ a/mm/compaction.c
@@ -1839,6 +1839,7 @@ static unsigned long fast_find_migratebl
 					pfn = cc->zone->zone_start_pfn;
 				cc->fast_search_fail = 0;
 				found_block = true;
+				set_pageblock_skip(freepage);

Patches currently in -mm which might be from are


             reply	other threads:[~2023-01-14  4:11 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-01-14  4:11 Andrew Morton [this message]
2023-01-16  5:46 ` + revert-mm-compaction-fix-set-skip-in-fast_find_migrateblock.patch added to mm-hotfixes-unstable branch Jiri Slaby

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