Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933292AbaJ2OEK (ORCPT ); Wed, 29 Oct 2014 10:04:10 -0400 Received: from cantor2.suse.de ([195.135.220.15]:43336 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932859AbaJ2OEH (ORCPT ); Wed, 29 Oct 2014 10:04:07 -0400 Message-ID: <5450F3D2.3070302@suse.cz> Date: Wed, 29 Oct 2014 15:04:02 +0100 From: Vlastimil Babka User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.1.0 MIME-Version: 1.0 To: Joonsoo Kim CC: linux-kernel@vger.kernel.org, akpm@linux-foundation.org, cl@linux.com, mgorman@suse.de, mina86@mina86.com, minchan@kernel.org, n-horiguchi@ah.jp.nec.com, riel@redhat.com, rientjes@google.com, zhangyanfei@cn.fujitsu.com, mm-commits@vger.kernel.org Subject: Re: + mm-compaction-avoid-premature-range-skip-in-isolate_migratepages_range.patch added to -mm tree References: <543d8d58.g9K7YpzF5ZOXeQqj%akpm@linux-foundation.org> <20141023081543.GB7598@js1304-P5Q-DELUXE> <5448BED1.40909@suse.cz> <20141024030006.GC15243@js1304-P5Q-DELUXE> In-Reply-To: <20141024030006.GC15243@js1304-P5Q-DELUXE> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/24/2014 05:00 AM, Joonsoo Kim wrote: > On Thu, Oct 23, 2014 at 10:39:45AM +0200, Vlastimil Babka wrote: >> On 10/23/2014 10:15 AM, Joonsoo Kim wrote: >>> On Tue, Oct 14, 2014 at 01:53:44PM -0700, akpm@linux-foundation.org wrote: >>>> >>>> The patch titled >>>> Subject: mm/compaction.c: avoid premature range skip in isolate_migratepages_range >>>> has been added to the -mm tree. Its filename is >>>> mm-compaction-avoid-premature-range-skip-in-isolate_migratepages_range.patch >>>> >>>> This patch should soon appear at >>>> http://ozlabs.org/~akpm/mmots/broken-out/mm-compaction-avoid-premature-range-skip-in-isolate_migratepages_range.patch >>>> and later at >>>> http://ozlabs.org/~akpm/mmotm/broken-out/mm-compaction-avoid-premature-range-skip-in-isolate_migratepages_range.patch >>>> >>>> Before you just go and hit "reply", please: >>>> a) Consider who else should be cc'ed >>>> b) Prefer to cc a suitable mailing list as well >>>> c) Ideally: find the original patch on the mailing list and do a >>>> reply-to-all to that, adding suitable additional cc's >>>> >>>> *** Remember to use Documentation/SubmitChecklist when testing your code *** >>>> >>>> The -mm tree is included into linux-next and is updated >>>> there every 3-4 working days >>>> >>>> ------------------------------------------------------ >>>> From: Joonsoo Kim >>>> Subject: mm/compaction.c: avoid premature range skip in isolate_migratepages_range >>>> >>>> commit edc2ca612496 ("mm, compaction: move pageblock checks up from >>>> isolate_migratepages_range()") commonizes isolate_migratepages variants >>>> and make them use isolate_migratepages_block(). >>>> >>>> isolate_migratepages_block() could stop the execution when enough pages >>>> are isolated, but, there is no code in isolate_migratepages_range() to >>>> handle this case. In the result, even if isolate_migratepages_block() >>>> returns prematurely without checking all pages in the range, >>>> >>>> isolate_migratepages_block() is called repeately on the following >>>> pageblock and some pages in the previous range are skipped to check. >>>> Then, CMA is failed frequently due to this fact. >>>> >>>> To fix this problem, this patch let isolate_migratepages_range() know the >>>> situation that enough pages are isolated and stop the isolation in that >>>> case. >>>> >>>> Note that isolate_migratepages() has no such problem, because, it always >>>> stops the isolation after just one call of isolate_migratepages_block(). >>>> >>>> Signed-off-by: Joonsoo Kim >>>> Cc: Vlastimil Babka >>>> Cc: David Rientjes >>>> Cc: Minchan Kim >>>> Cc: Michal Nazarewicz >>>> Cc: Naoya Horiguchi >>>> Cc: Christoph Lameter >>>> Cc: Rik van Riel >>>> Cc: Mel Gorman >>>> Cc: Zhang Yanfei >>>> Signed-off-by: Andrew Morton >> >> Acked-by: Vlastimil Babka >> >> Sorry for the trouble. But I think a more robust and future-proof fix >> would be a check such as: if (pfn < block_end_pfn) break; >> This should catch any reason where isolate_migratepages_block() did not >> finish whole pageblock, and which was not fatal enough to return pfn==0. >> However currently this seems to happen only due to isolating too much, >> so your patch should work. >> So it's up to you if you want to make the check more generic now, or >> later after this bug is fixed for 3.18. > > 'if (pfn < block_end_pfn) break;' has one problem. > If we have enough isolated pages and reach at block_end_pfn, > we can't stop with above check. Oh, right. > More proper check may be as following. > 'if (pfn < block_end_pfn || > cc->nr_migratepages == COMPACT_CLUSTER_MAX) break;' > But, as you mentioned, there is no case where 'pfn < block_end_pfn' > now, so I'd like to remain the patch as is. Yep, that would only make things uglier :/ So I'm for merging your patch in 3.18 cycle to prevent breakage. > Thanks. > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/