From: Joonsoo Kim <iamjoonsoo....@lge.com> It is odd to drop the spinlock when we scan (SWAP_CLUSTER_MAX - 1) th pfn page. This may results in below situation while isolating migratepage.
1. try isolate 0x0 ~ 0x200 pfn pages. 2. When low_pfn is 0x1ff, ((low_pfn+1) % SWAP_CLUSTER_MAX) == 0, so drop the spinlock. 3. Then, to complete isolating, retry to aquire the lock. I think that it is better to use SWAP_CLUSTER_MAX th pfn for checking the criteria about dropping the lock. This has no harm 0x0 pfn, because, at this time, locked variable would be false. Signed-off-by: Joonsoo Kim <iamjoonsoo....@lge.com> Acked-by: Vlastimil Babka <vba...@suse.cz> Cc: Mel Gorman <mgor...@suse.de> Cc: Rik van Riel <r...@redhat.com> Signed-off-by: Andrew Morton <a...@linux-foundation.org> Signed-off-by: Linus Torvalds <torva...@linux-foundation.org> (cherry picked from commit be1aa03b973c7dcdc576f3503f7a60429825c35d) Signed-off-by: Andrey Ryabinin <aryabi...@virtuozzo.com> --- mm/compaction.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/compaction.c b/mm/compaction.c index c29883fe146d..c4b6b134b197 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -494,7 +494,7 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc, cond_resched(); for (; low_pfn < end_pfn; low_pfn++) { /* give a chance to irqs before checking need_resched() */ - if (locked && !((low_pfn+1) % SWAP_CLUSTER_MAX)) { + if (locked && !(low_pfn % SWAP_CLUSTER_MAX)) { if (should_release_lock(&zone->lru_lock)) { spin_unlock_irqrestore(&zone->lru_lock, flags); locked = false; -- 2.13.6 _______________________________________________ Devel mailing list Devel@openvz.org https://lists.openvz.org/mailman/listinfo/devel