Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754838AbcDDJcF (ORCPT ); Mon, 4 Apr 2016 05:32:05 -0400 Received: from outbound-smtp04.blacknight.com ([81.17.249.35]:32847 "EHLO outbound-smtp04.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751338AbcDDJcD (ORCPT ); Mon, 4 Apr 2016 05:32:03 -0400 Date: Mon, 4 Apr 2016 10:31:59 +0100 From: Mel Gorman To: Vlastimil Babka Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Joonsoo Kim , Rik van Riel , David Rientjes , Minchan Kim , Michal Hocko Subject: Re: [PATCH v2 4/4] mm, compaction: direct freepage allocation for async direct compaction Message-ID: <20160404093159.GB4773@techsingularity.net> References: <1459414236-9219-1-git-send-email-vbabka@suse.cz> <1459414236-9219-5-git-send-email-vbabka@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <1459414236-9219-5-git-send-email-vbabka@suse.cz> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 765 Lines: 17 On Thu, Mar 31, 2016 at 10:50:36AM +0200, Vlastimil Babka wrote: > The goal of direct compaction is to quickly make a high-order page available > for the pending allocation. The free page scanner can add significant latency > when searching for migration targets, although to succeed the compaction, the > only important limit on the target free pages is that they must not come from > the same order-aligned block as the migrated pages. > What prevents the free pages being allocated from behind the migration scanner? Having compaction abort when the scanners meet misses compaction opportunities but it avoids the problem of Compactor A using pageblock X as a migration target and Compactor B using pageblock X as a migration source. -- Mel Gorman SUSE Labs