linux-kernel - Re: [PATCH 1/2] mm: vmscan: Avoid direct reclaim scanning at maximum priority

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Message-Id: <20130626123925.6a15ce3874fa4b0cc8390a0a@linux-foundation.org>
Date:	Wed, 26 Jun 2013 12:39:25 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Jiri Slaby <jslaby@...e.cz>,
	Valdis Kletnieks <Valdis.Kletnieks@...edu>,
	Rik van Riel <riel@...hat.com>,
	Zlatko Calusic <zcalusic@...sync.net>,
	Johannes Weiner <hannes@...xchg.org>,
	dormando <dormando@...ia.net>, Michal Hocko <mhocko@...e.cz>,
	Jan Kara <jack@...e.cz>, Dave Chinner <david@...morbit.com>,
	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Linux-FSDevel <linux-fsdevel@...r.kernel.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] mm: vmscan: Avoid direct reclaim scanning at
 maximum priority

On Wed, 26 Jun 2013 13:39:23 +0100 Mel Gorman <mgorman@...e.de> wrote:

> Page reclaim at priority 0 will scan the entire LRU as priority 0 is
> considered to be a near OOM condition. Direct reclaim can reach this
> priority while still making reclaim progress. This patch avoids
> reclaiming at priority 0 unless no reclaim progress was made and
> the page allocator would consider firing the OOM killer. The
> user-visible impact is that direct reclaim will not easily reach
> priority 0 and start swapping prematurely.

That's a bandaid.

Priority 0 should be a pretty darn rare condition.  How often is it
occurring, and do you know why?

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