Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753045Ab0HWN4P (ORCPT ); Mon, 23 Aug 2010 09:56:15 -0400 Received: from gir.skynet.ie ([193.1.99.77]:44175 "EHLO gir.skynet.ie" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751993Ab0HWN4O (ORCPT ); Mon, 23 Aug 2010 09:56:14 -0400 Date: Mon, 23 Aug 2010 14:55:59 +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 2/3] mm: page allocator: Calculate a better estimate of NR_FREE_PAGES when memory is low and kswapd is awake Message-ID: <20100823135559.GS19797@csn.ul.ie> References: <1282550442-15193-1-git-send-email-mel@csn.ul.ie> <1282550442-15193-3-git-send-email-mel@csn.ul.ie> <20100823130315.GQ19797@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: 1505 Lines: 33 On Mon, Aug 23, 2010 at 08:41:56AM -0500, Christoph Lameter wrote: > On Mon, 23 Aug 2010, Mel Gorman wrote: > > > > The delta of the counters could also be reduced to increase accuracy. > > > See refresh_zone_stat_thresholds(). > > True, but I thought that would introduce a constant performance penalty > > for a corner case which I didn't like. > > Sure, an increased frequency of updates would increase the chance of > bouncing cachelines. But the bouncing cacheline scenario for the vm > counters was tuned for applications that continually allocate pages in > parallel. > > When the vm gets into a state where continual reclaim is necessary then > the counters are not that frequently updated. If the machine is already > slowing down due to reclaim then the vm can likely affort more frequent > counter updates. > Ok, but is that better than this patch? Decreasing the size of the window by reducing the threshold still leaves a window. There is still a small amount of drift by summing up all the deltas but you get a much more accurate count at the point of time it was important to know. -- 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/