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 <vba...@suse.cz>
Reviewed-by: Zhang Yanfei <zhangyan...@cn.fujitsu.com>
Acked-by: Minchan Kim <minc...@kernel.org>
Acked-by: Mel Gorman <mgor...@suse.de>
Cc: Joonsoo Kim <iamjoonsoo....@lge.com>
Cc: Michal Nazarewicz <min...@mina86.com>
Cc: Naoya Horiguchi <n-horigu...@ah.jp.nec.com>
Cc: Christoph Lameter <c...@linux.com>
Cc: Rik van Riel <r...@redhat.com>
Acked-by: David Rientjes <rient...@google.com>
---
mm/compaction.c | 13 -------------
1 file changed, 13 deletions(-)
diff --git a/mm/compaction.c b/mm/compaction.c
index f3ae2ec..0a871e5 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -276,7 +276,6 @@ static unsigned long isolate_freepages_block(struct
compact_control *cc,
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_block(struct
compact_control *cc,
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;
--
1.8.4.5
--
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