From: Mel Gorman <mel@csn.ul.ie>
To: Christoph Lameter <cl@linux.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Linux Kernel List <linux-kernel@vger.kernel.org>,
linux-mm@kvack.org, Rik van Riel <riel@redhat.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Minchan Kim <minchan.kim@gmail.com>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Subject: Re: [PATCH 0/3] Reduce watermark-related problems with the per-cpu allocator V2
Date: Mon, 23 Aug 2010 14:01:27 +0100 [thread overview]
Message-ID: <20100823130127.GP19797@csn.ul.ie> (raw)
In-Reply-To: <alpine.DEB.2.00.1008230742300.4094@router.home>
On Mon, Aug 23, 2010 at 07:45:25AM -0500, Christoph Lameter wrote:
> On Mon, 23 Aug 2010, Mel Gorman wrote:
>
> > Internal IBM test teams beta testing distribution kernels have reported
> > problems on machines with a large number of CPUs whereby page allocator
> > failure messages show huge differences between the nr_free_pages vmstat
> > counter and what is available on the buddy lists. In an extreme example,
> > nr_free_pages was above the min watermark but zero pages were on the buddy
> > lists allowing the system to potentially livelock unable to make forward
> > progress unless an allocation succeeds. There is no reason why the problems
> > would not affect mainline so the following series mitigates the problems
> > in the page allocator related to to per-cpu counter drift and lists.
>
> 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.
--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab
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next prev parent reply other threads:[~2010-08-23 13:01 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-08-23 8:00 [PATCH 0/3] Reduce watermark-related problems with the per-cpu allocator V2 Mel Gorman
2010-08-23 8:00 ` [PATCH 1/3] mm: page allocator: Update free page counters after pages are placed on the free list Mel Gorman
2010-08-23 12:47 ` Christoph Lameter
2010-08-23 8:00 ` [PATCH 2/3] mm: page allocator: Calculate a better estimate of NR_FREE_PAGES when memory is low and kswapd is awake Mel Gorman
2010-08-23 12:56 ` Christoph Lameter
2010-08-23 13:03 ` Mel Gorman
2010-08-23 13:41 ` Christoph Lameter
2010-08-23 13:55 ` Mel Gorman
2010-08-23 16:04 ` Christoph Lameter
2010-08-23 16:13 ` Mel Gorman
2010-08-23 8:00 ` [PATCH 3/3] mm: page allocator: Drain per-cpu lists after direct reclaim allocation fails Mel Gorman
2010-08-23 23:17 ` KOSAKI Motohiro
2010-08-23 12:45 ` [PATCH 0/3] Reduce watermark-related problems with the per-cpu allocator V2 Christoph Lameter
2010-08-23 13:01 ` Mel Gorman [this message]
2010-08-23 13:38 ` Christoph Lameter
2010-08-23 13:39 ` Mel Gorman
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