From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with SMTP id 308846B0183 for ; Fri, 14 Oct 2011 08:25:11 -0400 (EDT) Date: Fri, 14 Oct 2011 07:25:06 -0500 From: Dimitri Sivanich Subject: Re: [PATCH] Reduce vm_stat cacheline contention in __vm_enough_memory Message-ID: <20111014122506.GB26737@sgi.com> References: <20111012160202.GA18666@sgi.com> <20111012120118.e948f40a.akpm@linux-foundation.org> <20111013152355.GB6966@sgi.com> <20111013135032.7c2c54cd.akpm@linux-foundation.org> <20111013142434.4d05cbdc.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20111013142434.4d05cbdc.akpm@linux-foundation.org> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Christoph Lameter , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Mel Gorman On Thu, Oct 13, 2011 at 02:24:34PM -0700, Andrew Morton wrote: > On Thu, 13 Oct 2011 16:02:58 -0500 (CDT) > Christoph Lameter wrote: > > > On Thu, 13 Oct 2011, Andrew Morton wrote: > > > > > > If there are no updates occurring for a while (due to increased deltas > > > > and/or vmstat updates) then the vm_stat cacheline should be able to stay > > > > in shared mode in multiple processors and the performance should increase. > > > > > > > > > > We could cacheline align vm_stat[]. But the thing is pretty small - we > > > couild put each entry in its own cacheline. > > > > Which in turn would increase the cache footprint of some key kernel > > functions (because they need multiple vm_stat entries) and cause eviction > > of other cachelines that then reduce overall system performance again. > > Sure, but we gain performance by not having different CPUs treading on > each other when they update different vmstat fields. Sometimes one > effect will win and other times the other effect will win. Some > engineering is needed.. I think the first step is to determine the role (if any) that false sharing may be playing in this, since that's a simpler fix (cacheline align and pad the array). Then, if necessary, will look at contention issues within the array. -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org