From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752707AbcGLIdu (ORCPT ); Tue, 12 Jul 2016 04:33:50 -0400 Received: from outbound-smtp09.blacknight.com ([46.22.139.14]:38237 "EHLO outbound-smtp09.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751931AbcGLIdr (ORCPT ); Tue, 12 Jul 2016 04:33:47 -0400 Date: Tue, 12 Jul 2016 09:33:42 +0100 From: Mel Gorman To: Hillf Danton Cc: "'Andrew Morton'" , "'Johannes Weiner'" , "'Vlastimil Babka'" , "'linux-kernel'" , linux-mm@kvack.org Subject: Re: [PATCH] mm, vmscan: Give up balancing node for high order allocations earlier Message-ID: <20160712083342.GC9806@techsingularity.net> References: <00ed01d1d1c8$fcb12ff0$f6138fd0$@alibaba-inc.com> <20160711152015.e3be8be7702fb0ca4625040d@linux-foundation.org> <013d01d1dc07$33896860$9a9c3920$@alibaba-inc.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <013d01d1dc07$33896860$9a9c3920$@alibaba-inc.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 12, 2016 at 02:32:45PM +0800, Hillf Danton wrote: > > > To avoid excessive reclaim, we give up rebalancing for high order > > > allocations right after reclaiming enough pages. > > > > hm. What are the observed runtime effects of this change? Any testing > > results? > > > This work was based on Mel's work, Sir, > "[PATCH 00/27] Move LRU page reclaim from zones to nodes v7". > I believe Andrew understands that but the question is what is the observed runtime effect of the patch? > In "[PATCH 06/27] mm, vmscan: Make kswapd reclaim in terms of nodes", > fragmentation detection is introduced to avoid excessive reclaim. We bail > out of balancing for high-order allocations if the pages reclaimed at the > __current__ reclaim priority are two times more than required. > > In this work we give up reclaiming for high-order allocations if the > __total__ number of pages reclaimed, from the first priority to the > current priority, is more than needed, and in net result we reclaim less > pages. > While it's clear what it does, it is not clear if it is an improvement. I had read the patch, considered merging it and decided against it. This decision was based on the fact the series did not appear to be over-reclaiming for high-order pages when compared with zone-lru. Did you test this patch with a workload that requires a lot of high-order pages and see if kswapd was over-reclaiming and that this patch addressed the issue? -- Mel Gorman SUSE Labs