From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f70.google.com (mail-ed1-f70.google.com [209.85.208.70]) by kanga.kvack.org (Postfix) with ESMTP id 23C376B0005 for ; Thu, 16 Aug 2018 05:25:16 -0400 (EDT) Received: by mail-ed1-f70.google.com with SMTP id t7-v6so1644514edh.20 for ; Thu, 16 Aug 2018 02:25:16 -0700 (PDT) Received: from outbound-smtp10.blacknight.com (outbound-smtp10.blacknight.com. [46.22.139.15]) by mx.google.com with ESMTPS id f12-v6si462830edq.89.2018.08.16.02.25.14 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 16 Aug 2018 02:25:14 -0700 (PDT) Received: from mail.blacknight.com (pemlinmail04.blacknight.ie [81.17.254.17]) by outbound-smtp10.blacknight.com (Postfix) with ESMTPS id 6D2111C2F22 for ; Thu, 16 Aug 2018 10:25:14 +0100 (IST) Date: Thu, 16 Aug 2018 10:25:08 +0100 From: Mel Gorman Subject: Re: [PATCH] mm, page_alloc: actually ignore mempolicies for high priority allocations Message-ID: <20180816092507.GA1719@techsingularity.net> References: <20180612122624.8045-1-vbabka@suse.cz> <20180815151652.05d4c4684b7dff2282b5c046@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20180815151652.05d4c4684b7dff2282b5c046@linux-foundation.org> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Vlastimil Babka , linux-kernel@vger.kernel.org, Michal Hocko , David Rientjes , Joonsoo Kim , linux-mm@kvack.org On Wed, Aug 15, 2018 at 03:16:52PM -0700, 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 FWIW, I thought I acked this already. Acked-by: Mel Gorman -- Mel Gorman SUSE Labs