Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751102AbdCPCSI (ORCPT ); Wed, 15 Mar 2017 22:18:08 -0400 Received: from LGEAMRELO11.lge.com ([156.147.23.51]:53470 "EHLO lgeamrelo11.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750858AbdCPCSH (ORCPT ); Wed, 15 Mar 2017 22:18:07 -0400 X-Original-SENDERIP: 156.147.1.125 X-Original-MAILFROM: iamjoonsoo.kim@lge.com X-Original-SENDERIP: 165.244.249.26 X-Original-MAILFROM: iamjoonsoo.kim@lge.com X-Original-SENDERIP: 10.177.222.138 X-Original-MAILFROM: iamjoonsoo.kim@lge.com Date: Thu, 16 Mar 2017 11:18:14 +0900 From: Joonsoo Kim To: Vlastimil Babka CC: Andrew Morton , , , Johannes Weiner , Mel Gorman , David Rientjes , , Subject: Re: [PATCH v3 8/8] mm, compaction: finish whole pageblock to reduce fragmentation Message-ID: <20170316021814.GD14063@js1304-P5Q-DELUXE> References: <20170307131545.28577-1-vbabka@suse.cz> <20170307131545.28577-9-vbabka@suse.cz> MIME-Version: 1.0 In-Reply-To: <20170307131545.28577-9-vbabka@suse.cz> User-Agent: Mutt/1.5.21 (2010-09-15) X-MIMETrack: Itemize by SMTP Server on LGEKRMHUB05/LGE/LG Group(Release 8.5.3FP6|November 21, 2013) at 2017/03/16 11:16:41, Serialize by Router on LGEKRMHUB05/LGE/LG Group(Release 8.5.3FP6|November 21, 2013) at 2017/03/16 11:16:41, Serialize complete at 2017/03/16 11:16:41 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3867 Lines: 89 On Tue, Mar 07, 2017 at 02:15:45PM +0100, Vlastimil Babka wrote: > The main goal of direct compaction is to form a high-order page for allocation, > but it should also help against long-term fragmentation when possible. Most > lower-than-pageblock-order compactions are for non-movable allocations, which > means that if we compact in a movable pageblock and terminate as soon as we > create the high-order page, it's unlikely that the fallback heuristics will > claim the whole block. Instead there might be a single unmovable page in a > pageblock full of movable pages, and the next unmovable allocation might pick > another pageblock and increase long-term fragmentation. > > To help against such scenarios, this patch changes the termination criteria for > compaction so that the current pageblock is finished even though the high-order > page already exists. Note that it might be possible that the high-order page > formed elsewhere in the zone due to parallel activity, but this patch doesn't > try to detect that. > > This is only done with sync compaction, because async compaction is limited to > pageblock of the same migratetype, where it cannot result in a migratetype > fallback. (Async compaction also eagerly skips order-aligned blocks where > isolation fails, which is against the goal of migrating away as much of the > pageblock as possible.) > > As a result of this patch, long-term memory fragmentation should be reduced. > > In testing based on 4.9 kernel with stress-highalloc from mmtests configured > for order-4 GFP_KERNEL allocations, this patch has reduced the number of > unmovable allocations falling back to movable pageblocks by 20%. The number > > Signed-off-by: Vlastimil Babka > Acked-by: Mel Gorman > Acked-by: Johannes Weiner > --- > mm/compaction.c | 36 ++++++++++++++++++++++++++++++++++-- > mm/internal.h | 1 + > 2 files changed, 35 insertions(+), 2 deletions(-) > > diff --git a/mm/compaction.c b/mm/compaction.c > index 2c288e75840d..bc7903130501 100644 > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -1318,6 +1318,17 @@ static enum compact_result __compact_finished(struct zone *zone, > if (is_via_compact_memory(cc->order)) > return COMPACT_CONTINUE; > > + if (cc->finishing_block) { > + /* > + * We have finished the pageblock, but better check again that > + * we really succeeded. > + */ > + if (IS_ALIGNED(cc->migrate_pfn, pageblock_nr_pages)) > + cc->finishing_block = false; > + else > + return COMPACT_CONTINUE; > + } > + > /* Direct compactor: Is a suitable page free? */ > for (order = cc->order; order < MAX_ORDER; order++) { > struct free_area *area = &zone->free_area[order]; > @@ -1338,8 +1349,29 @@ static enum compact_result __compact_finished(struct zone *zone, > * other migratetype buddy lists. > */ > if (find_suitable_fallback(area, order, migratetype, > - true, &can_steal) != -1) > - return COMPACT_SUCCESS; > + true, &can_steal) != -1) { > + > + /* movable pages are OK in any pageblock */ > + if (migratetype == MIGRATE_MOVABLE) > + return COMPACT_SUCCESS; > + > + /* > + * We are stealing for a non-movable allocation. Make > + * sure we finish compacting the current pageblock > + * first so it is as free as possible and we won't > + * have to steal another one soon. This only applies > + * to sync compaction, as async compaction operates > + * on pageblocks of the same migratetype. > + */ > + if (cc->mode == MIGRATE_ASYNC || > + IS_ALIGNED(cc->migrate_pfn, > + pageblock_nr_pages)) { > + return COMPACT_SUCCESS; > + } If cc->migratetype and cc->migrate_pfn's migratetype is the same, stopping the compaction here doesn't cause any fragmentation. Do we need to compact full pageblock in this case? Thanks.