linux-kernel - [PATCH] vmscan: comment too_many

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Message-ID: <20101022045554.GA17073@localhost>
Date:	Fri, 22 Oct 2010 12:55:54 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Neil Brown <neilb@...e.de>, Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"Li, Shaohua" <shaohua.li@...el.com>
Subject: [PATCH] vmscan: comment too_many_isolated()

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

Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Reviewed-by: Minchan Kim <minchan.kim@...il.com>
Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>
---
 mm/vmscan.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

--- linux-next.orig/mm/vmscan.c	2010-10-19 09:29:44.000000000 +0800
+++ linux-next/mm/vmscan.c	2010-10-19 10:21:41.000000000 +0800
@@ -1142,7 +1142,11 @@ 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)
--
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