The patch titled
Subject: mm, compaction: do not recheck suitable_migration_target under lock
has been added to the -mm tree. Its filename is
mm-compaction-do-not-recheck-suitable_migration_target-under-lock.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-compaction-do-not-recheck-suitable_migration_target-under-lock.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-compaction-do-not-recheck-suitable_migration_target-under-lock.patch
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From: Vlastimil Babka <vbabka@xxxxxxx>
Subject: mm, compaction: do not recheck suitable_migration_target under lock
isolate_freepages_block() rechecks if the pageblock is suitable to be a
target for migration after it has taken the zone->lock. However, the
check has been optimized to occur only once per pageblock, and
compact_checklock_irqsave() might be dropping and reacquiring lock, which
means somebody else might have changed the pageblock's migratetype
meanwhile.
Furthermore, nothing prevents the migratetype to change right after
isolate_freepages_block() has finished isolating. Given how imperfect
this is, it's simpler to just rely on the check done in
isolate_freepages() without lock, and not pretend that the recheck under
lock guarantees anything. It is just a heuristic after all.
Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
Reviewed-by: Zhang Yanfei <zhangyanfei@xxxxxxxxxxxxxx>
Acked-by: Minchan Kim <minchan@xxxxxxxxxx>
Acked-by: Mel Gorman <mgorman@xxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Michal Nazarewicz <mina86@xxxxxxxxxx>
Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/compaction.c | 13 -------------
1 file changed, 13 deletions(-)
diff -puN mm/compaction.c~mm-compaction-do-not-recheck-suitable_migration_target-under-lock mm/compaction.c
--- a/mm/compaction.c~mm-compaction-do-not-recheck-suitable_migration_target-under-lock
+++ a/mm/compaction.c
@@ -276,7 +276,6 @@ static unsigned long isolate_freepages_b
struct page *cursor, *valid_page = NULL;
unsigned long flags;
bool locked = false;
- bool checked_pageblock = false;
cursor = pfn_to_page(blockpfn);
@@ -307,18 +306,6 @@ static unsigned long isolate_freepages_b
if (!locked)
break;
- /* Recheck this is a suitable migration target under lock */
- if (!strict && !checked_pageblock) {
- /*
- * We need to check suitability of pageblock only once
- * and this isolate_freepages_block() is called with
- * pageblock range, so just check once is sufficient.
- */
- checked_pageblock = true;
- if (!suitable_migration_target(page))
- break;
- }
-
/* Recheck this is a buddy page under lock */
if (!PageBuddy(page))
goto isolate_fail;
_
Patches currently in -mm which might be from vbabka@xxxxxxx are
mm-page_alloc-determine-migratetype-only-once.patch
mm-thp-dont-hold-mmap_sem-in-khugepaged-when-allocating-thp.patch
mm-compaction-defer-each-zone-individually-instead-of-preferred-zone.patch
mm-compaction-do-not-count-compact_stall-if-all-zones-skipped-compaction.patch
mm-compaction-do-not-recheck-suitable_migration_target-under-lock.patch
mm-compaction-move-pageblock-checks-up-from-isolate_migratepages_range.patch
mm-compaction-reduce-zone-checking-frequency-in-the-migration-scanner.patch
mm-compaction-khugepaged-should-not-give-up-due-to-need_resched.patch
mm-compaction-periodically-drop-lock-and-restore-irqs-in-scanners.patch
mm-compaction-skip-rechecks-when-lock-was-already-held.patch
mm-compaction-remember-position-within-pageblock-in-free-pages-scanner.patch
mm-compaction-skip-buddy-pages-by-their-order-in-the-migrate-scanner.patch
mm-rename-allocflags_to_migratetype-for-clarity.patch
mm-compaction-pass-gfp-mask-to-compact_control.patch
mm-compactionc-isolate_freepages_block-small-tuneup.patch
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