From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935365AbcLTO2v (ORCPT ); Tue, 20 Dec 2016 09:28:51 -0500 Received: from outbound-smtp10.blacknight.com ([46.22.139.15]:55227 "EHLO outbound-smtp10.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933093AbcLTO2s (ORCPT ); Tue, 20 Dec 2016 09:28:48 -0500 Date: Tue, 20 Dec 2016 14:28:45 +0000 From: Mel Gorman To: Michal Hocko Cc: Jia He , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Vlastimil Babka , Johannes Weiner , Joonsoo Kim , Taku Izumi Subject: Re: [PATCH RFC 1/1] mm, page_alloc: fix incorrect zone_statistics data Message-ID: <20161220142845.drbedcibjcggdxk7@techsingularity.net> References: <1481522347-20393-1-git-send-email-hejianet@gmail.com> <1481522347-20393-2-git-send-email-hejianet@gmail.com> <20161220091814.GC3769@dhcp22.suse.cz> <20161220131040.f5ga5426dduh3mhu@techsingularity.net> <20161220132643.GG3769@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20161220132643.GG3769@dhcp22.suse.cz> User-Agent: Mutt/1.6.2 (2016-07-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 20, 2016 at 02:26:43PM +0100, Michal Hocko wrote: > On Tue 20-12-16 13:10:40, Mel Gorman wrote: > > On Tue, Dec 20, 2016 at 10:18:14AM +0100, Michal Hocko wrote: > > > On Mon 12-12-16 13:59:07, Jia He wrote: > > > > In commit b9f00e147f27 ("mm, page_alloc: reduce branches in > > > > zone_statistics"), it reconstructed codes to reduce the branch miss rate. > > > > Compared with the original logic, it assumed if !(flag & __GFP_OTHER_NODE) > > > > z->node would not be equal to preferred_zone->node. That seems to be > > > > incorrect. > > > > > > I am sorry but I have hard time following the changelog. It is clear > > > that you are trying to fix a missed NUMA_{HIT,OTHER} accounting > > > but it is not really clear when such thing happens. You are adding > > > preferred_zone->node check. preferred_zone is the first zone in the > > > requested zonelist. So for the most allocations it is a node from the > > > local node. But if something request an explicit numa node (without > > > __GFP_OTHER_NODE which would be the majority I suspect) then we could > > > indeed end up accounting that as a NUMA_MISS, NUMA_FOREIGN so the > > > referenced patch indeed caused an unintended change of accounting AFAIU. > > > > > > > This is a similar concern to what I had. If the preferred zone, which is > > the first valid usable zone, is not a "hit" for the statistics then I > > don't know what "hit" is meant to mean. > > But the first valid usable zone is defined based on the requested numa > node. Unless the requested node is memoryless then we should have a hit, > no? > Should be. If the local node is memoryless then there would be a difference between hit and whether it's local or not but that to me is a little useless. A local vs remote page allocated has a specific meaning and consequence. It's hard to see how hit can be meaningfully interpreted if there are memoryless nodes. I don't have a strong objection to the patch so I didn't nak it, I'm just not convinced it matters. -- Mel Gorman SUSE Labs