From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f69.google.com (mail-wm0-f69.google.com [74.125.82.69]) by kanga.kvack.org (Postfix) with ESMTP id 107616B007E for ; Wed, 4 May 2016 04:56:31 -0400 (EDT) Received: by mail-wm0-f69.google.com with SMTP id e201so42356927wme.1 for ; Wed, 04 May 2016 01:56:31 -0700 (PDT) Received: from mail-wm0-f65.google.com (mail-wm0-f65.google.com. [74.125.82.65]) by mx.google.com with ESMTPS id cb2si3571895wjc.188.2016.05.04.01.56.29 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 04 May 2016 01:56:30 -0700 (PDT) Received: by mail-wm0-f65.google.com with SMTP id w143so8992439wmw.3 for ; Wed, 04 May 2016 01:56:29 -0700 (PDT) Date: Wed, 4 May 2016 10:56:28 +0200 From: Michal Hocko Subject: Re: [PATCH 12/14] mm, oom: protect !costly allocations some more Message-ID: <20160504085628.GE29978@dhcp22.suse.cz> References: <1461181647-8039-1-git-send-email-mhocko@kernel.org> <1461181647-8039-13-git-send-email-mhocko@kernel.org> <20160504060123.GB10899@js1304-P5Q-DELUXE> <20160504063112.GD10899@js1304-P5Q-DELUXE> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160504063112.GD10899@js1304-P5Q-DELUXE> Sender: owner-linux-mm@kvack.org List-ID: To: Joonsoo Kim Cc: Andrew Morton , Linus Torvalds , Johannes Weiner , Mel Gorman , David Rientjes , Tetsuo Handa , Hillf Danton , Vlastimil Babka , linux-mm@kvack.org, LKML On Wed 04-05-16 15:31:12, Joonsoo Kim wrote: > On Wed, May 04, 2016 at 03:01:24PM +0900, Joonsoo Kim wrote: > > On Wed, Apr 20, 2016 at 03:47:25PM -0400, Michal Hocko wrote: [...] > > > @@ -3408,6 +3456,17 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, > > > no_progress_loops)) > > > goto retry; > > > > > > + /* > > > + * It doesn't make any sense to retry for the compaction if the order-0 > > > + * reclaim is not able to make any progress because the current > > > + * implementation of the compaction depends on the sufficient amount > > > + * of free memory (see __compaction_suitable) > > > + */ > > > + if (did_some_progress > 0 && > > > + should_compact_retry(order, compact_result, > > > + &migration_mode, compaction_retries)) > > > > Checking did_some_progress on each round have subtle corner case. Think > > about following situation. > > > > round, compaction, did_some_progress, compaction > > 0, defer, 1 > > 0, defer, 1 > > 0, defer, 1 > > 0, defer, 1 > > 0, defer, 0 > > Oops...Example should be below one. > > 0, defer, 1 > 1, defer, 1 > 2, defer, 1 > 3, defer, 1 > 4, defer, 0 I am not sure I understand. The point of the check is that if the reclaim doesn't make _any_ progress then checking the result of the compaction after it didn't lead to a successful allocation just doesn't make any sense. If the compaction deferred all the time then we have a bug in the compaction. Vlastimil is already working on a code which should make the compaction more ready for !costly requests but that is a separate topic IMO. -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org