From: Joonsoo Kim Date: Mon, 7 Apr 2014 22:37:05 +0000 (-0700) Subject: mm/compaction: change the timing to check to drop the spinlock X-Git-Tag: firefly_0821_release~176^2~4111^2~144 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=be1aa03b973c7dcdc576f3503f7a60429825c35d;p=firefly-linux-kernel-4.4.55.git mm/compaction: change the timing to check to drop the spinlock 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 Acked-by: Vlastimil Babka Cc: Mel Gorman Cc: Rik van Riel Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/mm/compaction.c b/mm/compaction.c index 3a1828541dc0..0eb9f99196ce 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -487,7 +487,7 @@ 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;