From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753203AbcEBIy1 (ORCPT ); Mon, 2 May 2016 04:54:27 -0400 Received: from mx2.suse.de ([195.135.220.15]:53221 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752231AbcEBIy0 (ORCPT ); Mon, 2 May 2016 04:54:26 -0400 Subject: Re: [PATCH 0/6] Optimise page alloc/free fast paths followup v2 To: Mel Gorman , Andrew Morton References: <1461769043-28337-1-git-send-email-mgorman@techsingularity.net> Cc: Jesper Dangaard Brouer , Linux-MM , LKML From: Vlastimil Babka Message-ID: <572715BF.3000003@suse.cz> Date: Mon, 2 May 2016 10:54:23 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.7.2 MIME-Version: 1.0 In-Reply-To: <1461769043-28337-1-git-send-email-mgorman@techsingularity.net> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/27/2016 04:57 PM, Mel Gorman wrote: > as the patch "mm, page_alloc: inline the fast path of the zonelist iterator" > is fine. The nodemask pointer is the same between cpuset retries. If the > zonelist changes due to ALLOC_NO_WATERMARKS *and* it races with a cpuset > change then there is a second harmless pass through the page allocator. True. But I just realized (while working on direct compaction priorities) that there's another subtle issue with the ALLOC_NO_WATERMARKS part. According to the comment it should be ignoring mempolicies, but it still honours ac.nodemask, and your patch is replacing NULL ac.nodemask with the mempolicy one. I think it's possibly easily fixed outside the fast path like this. If you agree, consider it has my s-o-b: diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 3f052bbca41d..7ccaa6e023f3 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -3834,6 +3834,11 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order, alloc_mask = memalloc_noio_flags(gfp_mask); ac.spread_dirty_pages = false; + /* + * Restore the original nodemask, which might have been replaced with + * &cpuset_current_mems_allowed to optimize the fast-path attempt. + */ + ac.nodemask = nodemask; page = __alloc_pages_slowpath(alloc_mask, order, &ac); no_zone: