From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=MAILING_LIST_MULTI,SPF_PASS, URIBL_BLOCKED,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C5BACC4321D for ; Thu, 16 Aug 2018 10:03:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7C31F20936 for ; Thu, 16 Aug 2018 10:03:23 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7C31F20936 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390684AbeHPNAs (ORCPT ); Thu, 16 Aug 2018 09:00:48 -0400 Received: from mx2.suse.de ([195.135.220.15]:46800 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727219AbeHPNAr (ORCPT ); Thu, 16 Aug 2018 09:00:47 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 01D72AF3B; Thu, 16 Aug 2018 10:03:18 +0000 (UTC) Date: Thu, 16 Aug 2018 12:03:17 +0200 From: Michal Hocko To: Andrew Morton Cc: Vlastimil Babka , linux-kernel@vger.kernel.org, Mel Gorman , David Rientjes , Joonsoo Kim , linux-mm@kvack.org Subject: Re: [PATCH] mm, page_alloc: actually ignore mempolicies for high priority allocations Message-ID: <20180816100317.GV32645@dhcp22.suse.cz> References: <20180612122624.8045-1-vbabka@suse.cz> <20180815151652.05d4c4684b7dff2282b5c046@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180815151652.05d4c4684b7dff2282b5c046@linux-foundation.org> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 15-08-18 15:16:52, Andrew Morton wrote: [...] > From: Vlastimil Babka > Subject: mm, page_alloc: actually ignore mempolicies for high priority allocations > > The __alloc_pages_slowpath() function has for a long time contained code > to ignore node restrictions from memory policies for high priority > allocations. The current code that resets the zonelist iterator however > does effectively nothing after commit 7810e6781e0f ("mm, page_alloc: do > not break __GFP_THISNODE by zonelist reset") removed a buggy zonelist > reset. Even before that commit, mempolicy restrictions were still not > ignored, as they are passed in ac->nodemask which is untouched by the > code. > > We can either remove the code, or make it work as intended. Since > ac->nodemask can be set from task's mempolicy via alloc_pages_current() > and thus also alloc_pages(), it may indeed affect kernel allocations, and > it makes sense to ignore it to allow progress for high priority > allocations. > > Thus, this patch resets ac->nodemask to NULL in such cases. This assumes > all callers can handle it (i.e. there are no guarantees as in the case of > __GFP_THISNODE) which seems to be the case. The same assumption is > already present in check_retry_cpuset() for some time. > > The expected effect is that high priority kernel allocations in the > context of userspace tasks (e.g. OOM victims) restricted by mempolicies > will have higher chance to succeed if they are restricted to nodes with > depleted memory, while there are other nodes with free memory left. > > > Ot's not a new intention, but for the first time the code will match the > intention, AFAICS. It was intended by commit 183f6371aac2 ("mm: ignore > mempolicies when using ALLOC_NO_WATERMARK") in v3.6 but I think it never > really worked, as mempolicy restriction was already encoded in nodemask, > not zonelist, at that time. > > So originally that was for ALLOC_NO_WATERMARK only. Then it was adjusted > by e46e7b77c909 ("mm, page_alloc: recalculate the preferred zoneref if the > context can ignore memory policies") and cd04ae1e2dc8 ("mm, oom: do not > rely on TIF_MEMDIE for memory reserves access") to the current state. So > even GFP_ATOMIC would now ignore mempolicies after the initial attempts > fail - if the code worked as people thought it does. > > Link: http://lkml.kernel.org/r/20180612122624.8045-1-vbabka@suse.cz > Signed-off-by: Vlastimil Babka > Cc: Mel Gorman > Cc: Michal Hocko > Cc: David Rientjes > Cc: Joonsoo Kim > Signed-off-by: Andrew Morton The code is quite subtle and we have a bad history of copying stuff without rethinking whether the code still is needed. Which is sad and a clear sign that the code is too complex. I cannot say this change doesn't have any subtle side effects but it makes the intention clear at least so I _think_ it is good to go. If we find some unintended side effects we should simply rethink the whole reset zonelist thing. That being said Acked-by: Michal Hocko > --- > > mm/page_alloc.c | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) > > --- a/mm/page_alloc.c~mm-page_alloc-actually-ignore-mempolicies-for-high-priority-allocations > +++ a/mm/page_alloc.c > @@ -4165,11 +4165,12 @@ retry: > alloc_flags = reserve_flags; > > /* > - * Reset the zonelist iterators if memory policies can be ignored. > - * These allocations are high priority and system rather than user > - * orientated. > + * Reset the nodemask and zonelist iterators if memory policies can be > + * ignored. These allocations are high priority and system rather than > + * user oriented. > */ > if (!(alloc_flags & ALLOC_CPUSET) || reserve_flags) { > + ac->nodemask = NULL; > ac->preferred_zoneref = first_zones_zonelist(ac->zonelist, > ac->high_zoneidx, ac->nodemask); > } > _ > -- Michal Hocko SUSE Labs