From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754262AbdBPLo0 (ORCPT ); Thu, 16 Feb 2017 06:44:26 -0500 Received: from gum.cmpxchg.org ([85.214.110.215]:35568 "EHLO gum.cmpxchg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753285AbdBPLoZ (ORCPT ); Thu, 16 Feb 2017 06:44:25 -0500 Date: Thu, 16 Feb 2017 06:44:10 -0500 From: Johannes Weiner To: Vlastimil Babka Cc: linux-mm@kvack.org, Joonsoo Kim , David Rientjes , Mel Gorman , linux-kernel@vger.kernel.org, kernel-team@fb.com Subject: Re: [PATCH v2 08/10] mm, compaction: finish whole pageblock to reduce fragmentation Message-ID: <20170216114410.GA15895@cmpxchg.org> References: <20170210172343.30283-1-vbabka@suse.cz> <20170210172343.30283-9-vbabka@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170210172343.30283-9-vbabka@suse.cz> User-Agent: Mutt/1.7.2 (2016-11-26) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Feb 10, 2017 at 06:23:41PM +0100, Vlastimil Babka wrote: > The main goal of direct compaction is to form a high-order page for allocation, > but it should also help against long-term fragmentation when possible. Most > lower-than-pageblock-order compactions are for non-movable allocations, which > means that if we compact in a movable pageblock and terminate as soon as we > create the high-order page, it's unlikely that the fallback heuristics will > claim the whole block. Instead there might be a single unmovable page in a > pageblock full of movable pages, and the next unmovable allocation might pick > another pageblock and increase long-term fragmentation. > > To help against such scenarios, this patch changes the termination criteria for > compaction so that the current pageblock is finished even though the high-order > page already exists. Note that it might be possible that the high-order page > formed elsewhere in the zone due to parallel activity, but this patch doesn't > try to detect that. > > This is only done with sync compaction, because async compaction is limited to > pageblock of the same migratetype, where it cannot result in a migratetype > fallback. (Async compaction also eagerly skips order-aligned blocks where > isolation fails, which is against the goal of migrating away as much of the > pageblock as possible.) > > As a result of this patch, long-term memory fragmentation should be reduced. > > Signed-off-by: Vlastimil Babka Acked-by: Johannes Weiner