From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail191.messagelabs.com (mail191.messagelabs.com [216.82.242.19]) by kanga.kvack.org (Postfix) with ESMTP id 4AE336B03BA for ; Mon, 23 Aug 2010 09:03:46 -0400 (EDT) Date: Mon, 23 Aug 2010 14:03:16 +0100 From: Mel Gorman 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: <20100823130315.GQ19797@csn.ul.ie> References: <1282550442-15193-1-git-send-email-mel@csn.ul.ie> <1282550442-15193-3-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: Sender: owner-linux-mm@kvack.org To: Christoph Lameter Cc: Andrew Morton , Linux Kernel List , linux-mm@kvack.org, Rik van Riel , Johannes Weiner , Minchan Kim , KAMEZAWA Hiroyuki , KOSAKI Motohiro List-ID: On Mon, Aug 23, 2010 at 07:56:40AM -0500, Christoph Lameter wrote: > On Mon, 23 Aug 2010, Mel Gorman wrote: > > > This patch introduces zone_nr_free_pages() to take a slightly more accurate > > estimate of NR_FREE_PAGES while kswapd is awake. The estimate is not perfect > > and may result in cache line bounces but is expected to be lighter than the > > IPI calls necessary to continually drain the per-cpu counters while kswapd > > is awake. > > 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. > Also would it be possible to add the summation function to vmstat? It may > be useful elsewhere. > > A new function like > > zone_page_state_snapshot() > > or so? > We could if there is another counter that results in bad system behaviour due to counter drift. As NR_FREE_PAGES seemed to be the only one, zone_nr_free_pages() seemed adequate. If such a helper did exist, zone_nr_free_pages() would be a simple wrapper around it. The indirection didn't seem necessary at this point though. -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org