[RFC 01/13] mm, compaction: don't isolate PageWriteback pages in MIGRATE_SYNC_LIGHT mode

Vlastimil Babka
2016-05-10T07:37:14Z

From: Hugh Dickins <hughd@google.com>

At present MIGRATE_SYNC_LIGHT is allowing __isolate_lru_page() to
isolate a PageWriteback page, which __unmap_and_move() then rejects
with -EBUSY: of course the writeback might complete in between, but
that's not what we usually expect, so probably better not to isolate it.

Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
---
mm/compaction.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index c72987603343..481004c73c90 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1146,7 +1146,7 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
struct page *page;
const isolate_mode_t isolate_mode =
(sysctl_compact_unevictable_allowed ? ISOLATE_UNEVICTABLE : 0) |
- (cc->mode == MIGRATE_ASYNC ? ISOLATE_ASYNC_MIGRATE : 0);
+ (cc->mode != MIGRATE_SYNC ? ISOLATE_ASYNC_MIGRATE : 0);

/*
* Start at where we last stopped, or beginning of the zone as
--
2.8.2