linux-kernel - Re: [PATCH 0/3] Reduce watermark-related problems with the per-cpu allocator V2

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Message-ID: <alpine.DEB.2.00.1008230835220.5750@router.home>
Date:	Mon, 23 Aug 2010 08:38:25 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Mel Gorman <mel@....ul.ie>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel List <linux-kernel@...r.kernel.org>,
	linux-mm@...ck.org, Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Minchan Kim <minchan.kim@...il.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Subject: Re: [PATCH 0/3] Reduce watermark-related problems with the per-cpu
 allocator V2

On Mon, 23 Aug 2010, Mel Gorman wrote:

> > The maximum time for which the livelock can exists is the vm stat
> > interval. By default the counters are brought up to date at least once per
> > second or if a certain delta was violated. Drifts are controlled by the
> > delta configuration.
> >
>
> While there is a maximum time (2 seconds I think) the drift can exist
> in, a machine under enough pressure can make a mess of the watermarks
> during that time. If it wasn't the case, these livelocks with 0 pages
> free wouldn't be happening.

So because we go way beyond the watermarks we reach a state in which a
livelock exists that does not go away when the counters are finally
updated?


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