From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751736AbcHPGBt (ORCPT ); Tue, 16 Aug 2016 02:01:49 -0400 Received: from LGEAMRELO13.lge.com ([156.147.23.53]:59228 "EHLO lgeamrelo13.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750940AbcHPGBs (ORCPT ); Tue, 16 Aug 2016 02:01:48 -0400 X-Original-SENDERIP: 156.147.1.151 X-Original-MAILFROM: iamjoonsoo.kim@lge.com X-Original-SENDERIP: 10.177.222.138 X-Original-MAILFROM: iamjoonsoo.kim@lge.com Date: Tue, 16 Aug 2016 15:07:37 +0900 From: Joonsoo Kim To: Vlastimil Babka Cc: Andrew Morton , Michal Hocko , Mel Gorman , David Rientjes , Rik van Riel , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v6 06/11] mm, compaction: more reliably increase direct compaction priority Message-ID: <20160816060737.GC17448@js1304-P5Q-DELUXE> References: <20160810091226.6709-1-vbabka@suse.cz> <20160810091226.6709-7-vbabka@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160810091226.6709-7-vbabka@suse.cz> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Aug 10, 2016 at 11:12:21AM +0200, Vlastimil Babka wrote: > During reclaim/compaction loop, compaction priority can be increased by the > should_compact_retry() function, but the current code is not optimal. Priority > is only increased when compaction_failed() is true, which means that compaction > has scanned the whole zone. This may not happen even after multiple attempts > with a lower priority due to parallel activity, so we might needlessly > struggle on the lower priorities and possibly run out of compaction retry > attempts in the process. > > After this patch we are guaranteed at least one attempt at the highest > compaction priority even if we exhaust all retries at the lower priorities. The only difference that this patch makes is increasing priority when COMPACT_PARTIAL(COMPACTION_SUCCESS) returns. In that case, we can usually allocate high-order freepage so we would not enter here. Am I missing something? Is it really needed behaviour change? Thanks. > > Signed-off-by: Vlastimil Babka > --- > mm/page_alloc.c | 18 +++++++++++------- > 1 file changed, 11 insertions(+), 7 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index fb975cec3518..b28517b918b0 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -3155,13 +3155,8 @@ should_compact_retry(struct alloc_context *ac, int order, int alloc_flags, > * so it doesn't really make much sense to retry except when the > * failure could be caused by insufficient priority > */ > - if (compaction_failed(compact_result)) { > - if (*compact_priority > MIN_COMPACT_PRIORITY) { > - (*compact_priority)--; > - return true; > - } > - return false; > - } > + if (compaction_failed(compact_result)) > + goto check_priority; > > /* > * make sure the compaction wasn't deferred or didn't bail out early > @@ -3185,6 +3180,15 @@ should_compact_retry(struct alloc_context *ac, int order, int alloc_flags, > if (compaction_retries <= max_retries) > return true; > > + /* > + * Make sure there is at least one attempt at the highest priority > + * if we exhausted all retries at the lower priorities > + */ > +check_priority: > + if (*compact_priority > MIN_COMPACT_PRIORITY) { > + (*compact_priority)--; > + return true; > + } > return false; The only difference that this patch makes is increasing priority when COMPACT_PARTIAL(COMPACTION_SUCCESS) returns. In that case, we can usually allocate high-order freepage so we would not enter here. Am I missing something? Is it really needed behaviour change? Thanks.