Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752792Ab0HWNBn (ORCPT ); Mon, 23 Aug 2010 09:01:43 -0400 Received: from gir.skynet.ie ([193.1.99.77]:34647 "EHLO gir.skynet.ie" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751805Ab0HWNBl (ORCPT ); Mon, 23 Aug 2010 09:01:41 -0400 Date: Mon, 23 Aug 2010 14:01:27 +0100 From: Mel Gorman To: Christoph Lameter Cc: Andrew Morton , Linux Kernel List , linux-mm@kvack.org, Rik van Riel , Johannes Weiner , Minchan Kim , KAMEZAWA Hiroyuki , KOSAKI Motohiro Subject: Re: [PATCH 0/3] Reduce watermark-related problems with the per-cpu allocator V2 Message-ID: <20100823130127.GP19797@csn.ul.ie> References: <1282550442-15193-1-git-send-email-mel@csn.ul.ie> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17+20080114 (2008-01-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1692 Lines: 33 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/