From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751889AbcGRJXo (ORCPT ); Mon, 18 Jul 2016 05:23:44 -0400 Received: from mx2.suse.de ([195.135.220.15]:56977 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751452AbcGRJXm (ORCPT ); Mon, 18 Jul 2016 05:23:42 -0400 Subject: Re: [PATCH v3 13/17] mm, compaction: use correct watermark when checking allocation success To: Joonsoo Kim References: <20160624095437.16385-1-vbabka@suse.cz> <20160624095437.16385-14-vbabka@suse.cz> <20160706054722.GF23627@js1304-P5Q-DELUXE> Cc: Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Michal Hocko , Mel Gorman , David Rientjes , Rik van Riel From: Vlastimil Babka Message-ID: Date: Mon, 18 Jul 2016 11:23:38 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.1.1 MIME-Version: 1.0 In-Reply-To: <20160706054722.GF23627@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 07/06/2016 07:47 AM, Joonsoo Kim wrote: > On Fri, Jun 24, 2016 at 11:54:33AM +0200, Vlastimil Babka wrote: >> The __compact_finished() function uses low watermark in a check that has to >> pass if the direct compaction is to finish and allocation should succeed. This >> is too pessimistic, as the allocation will typically use min watermark. It may >> happen that during compaction, we drop below the low watermark (due to parallel >> activity), but still form the target high-order page. By checking against low >> watermark, we might needlessly continue compaction. >> >> Similarly, __compaction_suitable() uses low watermark in a check whether >> allocation can succeed without compaction. Again, this is unnecessarily >> pessimistic. >> >> After this patch, these check will use direct compactor's alloc_flags to >> determine the watermark, which is effectively the min watermark. >> >> Signed-off-by: Vlastimil Babka >> Acked-by: Michal Hocko >> --- >> mm/compaction.c | 6 +++--- >> 1 file changed, 3 insertions(+), 3 deletions(-) >> >> diff --git a/mm/compaction.c b/mm/compaction.c >> index 76897850c3c2..371760a85085 100644 >> --- a/mm/compaction.c >> +++ b/mm/compaction.c >> @@ -1320,7 +1320,7 @@ static enum compact_result __compact_finished(struct zone *zone, struct compact_ >> return COMPACT_CONTINUE; >> >> /* Compaction run is not finished if the watermark is not met */ >> - watermark = low_wmark_pages(zone); >> + watermark = zone->watermark[cc->alloc_flags & ALLOC_WMARK_MASK]; > > finish condition is changed. We have two more watermark checks in > try_to_compact_pages() and kcompactd_do_work() and they should be > changed too. Ugh, I've completely missed them. Thanks for catching this, hopefully fixing that will improve the results.