Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752454AbbBSAEI (ORCPT ); Wed, 18 Feb 2015 19:04:08 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:48578 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752126AbbBSAEH (ORCPT ); Wed, 18 Feb 2015 19:04:07 -0500 Date: Wed, 18 Feb 2015 16:04:05 -0800 From: Andrew Morton To: Joonsoo Kim Cc: Vlastimil Babka , Mel Gorman , David Rientjes , Rik van Riel , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Zhang Yanfei Subject: Re: [PATCH v4 3/3] mm/compaction: enhance compaction finish condition Message-Id: <20150218160405.526418167249559d0ed3efc5@linux-foundation.org> In-Reply-To: <1423725305-3726-3-git-send-email-iamjoonsoo.kim@lge.com> References: <1423725305-3726-1-git-send-email-iamjoonsoo.kim@lge.com> <1423725305-3726-3-git-send-email-iamjoonsoo.kim@lge.com> X-Mailer: Sylpheed 3.4.1 (GTK+ 2.24.23; 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 List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4315 Lines: 95 On Thu, 12 Feb 2015 16:15:05 +0900 Joonsoo Kim wrote: > Compaction has anti fragmentation algorithm. It is that freepage > should be more than pageblock order to finish the compaction if we don't > find any freepage in requested migratetype buddy list. This is for > mitigating fragmentation, but, there is a lack of migratetype > consideration and it is too excessive compared to page allocator's anti > fragmentation algorithm. > > Not considering migratetype would cause premature finish of compaction. > For example, if allocation request is for unmovable migratetype, > freepage with CMA migratetype doesn't help that allocation and > compaction should not be stopped. But, current logic regards this > situation as compaction is no longer needed, so finish the compaction. > > Secondly, condition is too excessive compared to page allocator's logic. > We can steal freepage from other migratetype and change pageblock > migratetype on more relaxed conditions in page allocator. This is designed > to prevent fragmentation and we can use it here. Imposing hard constraint > only to the compaction doesn't help much in this case since page allocator > would cause fragmentation again. > > To solve these problems, this patch borrows anti fragmentation logic from > page allocator. It will reduce premature compaction finish in some cases > and reduce excessive compaction work. > > stress-highalloc test in mmtests with non movable order 7 allocation shows > considerable increase of compaction success rate. > > Compaction success rate (Compaction success * 100 / Compaction stalls, %) > 31.82 : 42.20 > > I tested it on non-reboot 5 runs stress-highalloc benchmark and found that > there is no more degradation on allocation success rate than before. That > roughly means that this patch doesn't result in more fragmentations. > > Vlastimil suggests additional idea that we only test for fallbacks > when migration scanner has scanned a whole pageblock. It looked good for > fragmentation because chance of stealing increase due to making more > free pages in certain pageblock. So, I tested it, but, it results in > decreased compaction success rate, roughly 38.00. I guess the reason that > if system is low memory condition, watermark check could be failed due to > not enough order 0 free page and so, sometimes, we can't reach a fallback > check although migrate_pfn is aligned to pageblock_nr_pages. I can insert > code to cope with this situation but it makes code more complicated so > I don't include his idea at this patch. > > ... > > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -1170,13 +1170,23 @@ static int __compact_finished(struct zone *zone, struct compact_control *cc, > /* Direct compactor: Is a suitable page free? */ > for (order = cc->order; order < MAX_ORDER; order++) { > struct free_area *area = &zone->free_area[order]; > + bool can_steal; > > /* Job done if page is free of the right migratetype */ > if (!list_empty(&area->free_list[migratetype])) > return COMPACT_PARTIAL; > > - /* Job done if allocation would set block type */ > - if (order >= pageblock_order && area->nr_free) > + /* MIGRATE_MOVABLE can fallback on MIGRATE_CMA */ > + if (migratetype == MIGRATE_MOVABLE && > + !list_empty(&area->free_list[MIGRATE_CMA])) > + return COMPACT_PARTIAL; MIGRATE_CMA isn't defined if CONFIG_CMA=n. --- a/mm/compaction.c~mm-compaction-enhance-compaction-finish-condition-fix +++ a/mm/compaction.c @@ -1180,11 +1180,12 @@ static int __compact_finished(struct zon if (!list_empty(&area->free_list[migratetype])) return COMPACT_PARTIAL; +#ifdef CONFIG_CMA /* MIGRATE_MOVABLE can fallback on MIGRATE_CMA */ if (migratetype == MIGRATE_MOVABLE && !list_empty(&area->free_list[MIGRATE_CMA])) return COMPACT_PARTIAL; - +#endif /* * Job done if allocation would steal freepages from * other migratetype buddy lists. Please review the rest of the patchset for the CONFIG_CMA=n case (is it all necessary?), runtime test it and let me know? -- 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/