From: Fengguang Wu <fengguang.wu@intel.com>
Date: Tue, 18 Dec 2012 22:23:28 +0000 (-0800)
Subject: vmscan: comment too_many_isolated()
X-Git-Url: http://git.lede-project.org./?a=commitdiff_plain;h=d37dd5dcb955dd8c2cdd4eaef1f15d1b7ecbc379;p=openwrt%2Fstaging%2Fblogic.git

vmscan: comment too_many_isolated()

Comment "Why it's doing so" rather than "What it does" as proposed by
Andrew Morton.

Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Reviewed-by: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 7f3096137b8a..e73d0206dddd 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1177,7 +1177,11 @@ int isolate_lru_page(struct page *page)
 }
 
 /*
- * Are there way too many processes in the direct reclaim path already?
+ * A direct reclaimer may isolate SWAP_CLUSTER_MAX pages from the LRU list and
+ * then get resheduled. When there are massive number of tasks doing page
+ * allocation, such sleeping direct reclaimers may keep piling up on each CPU,
+ * the LRU list will go small and be scanned faster than necessary, leading to
+ * unnecessary swapping, thrashing and OOM.
  */
 static int too_many_isolated(struct zone *zone, int file,
 		struct scan_control *sc)