From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f172.google.com (mail-wi0-f172.google.com [209.85.212.172]) by kanga.kvack.org (Postfix) with ESMTP id A8DCA6B006C for ; Mon, 8 Dec 2014 06:07:19 -0500 (EST) Received: by mail-wi0-f172.google.com with SMTP id n3so4340280wiv.5 for ; Mon, 08 Dec 2014 03:07:19 -0800 (PST) Received: from mx2.suse.de (cantor2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id l3si9283712wic.38.2014.12.08.03.07.18 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Mon, 08 Dec 2014 03:07:18 -0800 (PST) Date: Mon, 8 Dec 2014 11:07:14 +0000 From: Mel Gorman Subject: Re: [RFC PATCH 1/3] mm: when stealing freepages, also take pages created by splitting buddy page Message-ID: <20141208110714.GN6043@suse.de> References: <1417713178-10256-1-git-send-email-vbabka@suse.cz> <1417713178-10256-2-git-send-email-vbabka@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <1417713178-10256-2-git-send-email-vbabka@suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Vlastimil Babka Cc: linux-mm@kvack.org, Joonsoo Kim , linux-kernel@vger.kernel.org, Minchan Kim , Rik van Riel , David Rientjes On Thu, Dec 04, 2014 at 06:12:56PM +0100, Vlastimil Babka wrote: > When __rmqueue_fallback() is called to allocate a page of order X, it will > find a page of order Y >= X of a fallback migratetype, which is different from > the desired migratetype. With the help of try_to_steal_freepages(), it may > change the migratetype (to the desired one) also of: > > 1) all currently free pages in the pageblock containing the fallback page > 2) the fallback pageblock itself > 3) buddy pages created by splitting the fallback page (when Y > X) > > These decisions take the order Y into account, as well as the desired > migratetype, with the goal of preventing multiple fallback allocations that > could e.g. distribute UNMOVABLE allocations among multiple pageblocks. > > Originally, decision for 1) has implied the decision for 3). Commit > 47118af076f6 ("mm: mmzone: MIGRATE_CMA migration type added") changed that > (probably unintentionally) so that the buddy pages in case 3) are always > changed to the desired migratetype, except for CMA pageblocks. > > Commit fef903efcf0c ("mm/page_allo.c: restructure free-page stealing code and > fix a bug") did some refactoring and added a comment that the case of 3) is > intended. Commit 0cbef29a7821 ("mm: __rmqueue_fallback() should respect > pageblock type") removed the comment and tried to restore the original behavior > where 1) implies 3), but due to the previous refactoring, the result is instead > that only 2) implies 3) - and the conditions for 2) are less frequently met > than conditions for 1). This may increase fragmentation in situations where the > code decides to steal all free pages from the pageblock (case 1)), but then > gives back the buddy pages produced by splitting. > > This patch restores the original intended logic where 1) implies 3). During > testing with stress-highalloc from mmtests, this has shown to decrease the > number of events where UNMOVABLE and RECLAIMABLE allocations steal from MOVABLE > pageblocks, which can lead to permanent fragmentation. It has increased the > number of events when MOVABLE allocations steal from UNMOVABLE or RECLAIMABLE > pageblocks, but these are fixable by sync compaction and thus less harmful. > > Signed-off-by: Vlastimil Babka Assuming the tracepoint issue Joonsoo pointed out gets corrected; Acked-by: Mel Gorman I'm kicking myself that I missed the effect of 47118af076f6 when I was reviewing it. I knew allocation success rates were worse than they used to be but had been blaming changes in aggression of reclaim and compaction. -- 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