From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f72.google.com (mail-wm0-f72.google.com [74.125.82.72]) by kanga.kvack.org (Postfix) with ESMTP id EC4006B032A for ; Tue, 20 Dec 2016 09:54:37 -0500 (EST) Received: by mail-wm0-f72.google.com with SMTP id m203so25478931wma.2 for ; Tue, 20 Dec 2016 06:54:37 -0800 (PST) Received: from outbound-smtp06.blacknight.com (outbound-smtp06.blacknight.com. [81.17.249.39]) by mx.google.com with ESMTPS id fq2si23031436wjb.119.2016.12.20.06.54.36 for (version=TLS1 cipher=AES128-SHA bits=128/128); Tue, 20 Dec 2016 06:54:36 -0800 (PST) Received: from mail.blacknight.com (pemlinmail01.blacknight.ie [81.17.254.10]) by outbound-smtp06.blacknight.com (Postfix) with ESMTPS id 2F1C6C244 for ; Tue, 20 Dec 2016 14:54:36 +0000 (UTC) Date: Tue, 20 Dec 2016 14:54:35 +0000 From: Mel Gorman Subject: Re: [PATCH RFC 1/1] mm, page_alloc: fix incorrect zone_statistics data Message-ID: <20161220145435.c3htqyfhpjt5uma7@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> <20161220142845.drbedcibjcggdxk7@techsingularity.net> <20161220143501.GI3769@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20161220143501.GI3769@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: 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 On Tue, Dec 20, 2016 at 03:35:02PM +0100, Michal Hocko wrote: > On Tue 20-12-16 14:28:45, Mel Gorman wrote: > > 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. > > So what do you think about > http://lkml.kernel.org/r/20161220091814.GC3769@dhcp22.suse.cz > This doesn't appear to resolve for me and I've 30 minutes left before being offline for 4 days so didn't go digging. > I think that we should get rid of __GFP_OTHER_NODE thingy. It is just > one off thing and the gfp space it rather precious. > However, broadly speaking, I'd be ok with getting rid of __GFP_OTHER_NODE altogether and making it truely only about local vs remote hits because those are the ones that matter in terms of performance. If a user has memoryless nodes or policies that allow local CPUs but forbid local memory and they need to debug an issue, they're going to need tracepoints anyway. Hit/miss/other is not sufficient for most interesting problems involving local or remote memory usage. -- Mel Gorman SUSE Labs -- 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