From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753435AbcEWIU3 (ORCPT ); Mon, 23 May 2016 04:20:29 -0400 Received: from mx2.suse.de ([195.135.220.15]:51545 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753028AbcEWIU1 (ORCPT ); Mon, 23 May 2016 04:20:27 -0400 Subject: Re: [PATCH] mm: compact: remove watermark check at compact suitable To: Chen Feng , akpm@linux-foundation.org, iamjoonsoo.kim@lge.com, mina86@mina86.com, rientjes@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1463973617-10599-1-git-send-email-puck.chen@hisilicon.com> Cc: xuyiping@hisilicon.com, suzhuangluan@hisilicon.com, dan.zhao@hisilicon.com, qijiwen@hisilicon.com, oliver.fu@hisilicon.com, puck.chen@foxmail.com From: Vlastimil Babka Message-ID: <5742BD46.8050403@suse.cz> Date: Mon, 23 May 2016 10:20:22 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.7.1 MIME-Version: 1.0 In-Reply-To: <1463973617-10599-1-git-send-email-puck.chen@hisilicon.com> Content-Type: text/plain; charset=iso-8859-2; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/23/2016 05:20 AM, Chen Feng wrote: > There are two paths calling this function. > For direct compact, there is no need to check the zone watermark here. > For kswapd wakeup kcompactd, since there is a reclaim before this. > It makes sense to do compact even the watermark is ok at this time. Hi, I'm just working on v2 of the series [1] and some patches planned for v2 are trying to simplify the watermark checks around compaction. The check you are removing looked like simple and obvious one, so I didn't change it. But I'll think more about your patch, e.g. if there are some corner cases. See for example the fragindex check: * index of -1000 would imply allocations might succeed depending on * watermarks, but we already failed the high-order watermark check After your patch, there is no more high-order watermark check, so the assumption here is gone. Also the comment above __compaction_suitable() should be updated too. [1] http://lkml.kernel.org/r/<1462865763-22084-1-git-send-email-vbabka@suse.cz> > Signed-off-by: Chen Feng > --- > mm/compaction.c | 7 ------- > 1 file changed, 7 deletions(-) > > diff --git a/mm/compaction.c b/mm/compaction.c > index 8fa2540..cb322df 100644 > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -1260,13 +1260,6 @@ static unsigned long __compaction_suitable(struct zone *zone, int order, > return COMPACT_CONTINUE; > > watermark = low_wmark_pages(zone); > - /* > - * If watermarks for high-order allocation are already met, there > - * should be no need for compaction at all. > - */ > - if (zone_watermark_ok(zone, order, watermark, classzone_idx, > - alloc_flags)) > - return COMPACT_PARTIAL; > > /* > * Watermarks for order-0 must be met for compaction. Note the 2UL. >