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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED 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 2A95AC4321D for ; Wed, 15 Aug 2018 22:16:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3B8192152A for ; Wed, 15 Aug 2018 22:16:57 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3B8192152A Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.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 S1728043AbeHPBK7 (ORCPT ); Wed, 15 Aug 2018 21:10:59 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:38406 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726957AbeHPBK7 (ORCPT ); Wed, 15 Aug 2018 21:10:59 -0400 Received: from akpm3.svl.corp.google.com (unknown [104.133.9.92]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id 4C8E6D5A; Wed, 15 Aug 2018 22:16:53 +0000 (UTC) Date: Wed, 15 Aug 2018 15:16:52 -0700 From: Andrew Morton To: Vlastimil Babka Cc: linux-kernel@vger.kernel.org, Mel Gorman , Michal Hocko , David Rientjes , Joonsoo Kim , linux-mm@kvack.org Subject: Re: [PATCH] mm, page_alloc: actually ignore mempolicies for high priority allocations Message-Id: <20180815151652.05d4c4684b7dff2282b5c046@linux-foundation.org> In-Reply-To: <20180612122624.8045-1-vbabka@suse.cz> References: <20180612122624.8045-1-vbabka@suse.cz> X-Mailer: Sylpheed 3.6.0 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 12 Jun 2018 14:26:24 +0200 Vlastimil Babka wrote: > 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. We don't have any reviews or acks on ths one, perhaps because linux-mm wasn't cc'ed. Could people please take a look? 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 --- 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); } _