Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756679AbcJNB0b (ORCPT ); Thu, 13 Oct 2016 21:26:31 -0400 Received: from LGEAMRELO11.lge.com ([156.147.23.51]:34009 "EHLO lgeamrelo11.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752495AbcJNB0X (ORCPT ); Thu, 13 Oct 2016 21:26:23 -0400 X-Original-SENDERIP: 156.147.1.126 X-Original-MAILFROM: iamjoonsoo.kim@lge.com X-Original-SENDERIP: 10.177.222.138 X-Original-MAILFROM: iamjoonsoo.kim@lge.com Date: Fri, 14 Oct 2016 10:26:16 +0900 From: Joonsoo Kim To: Vlastimil Babka Cc: Andrew Morton , Johannes Weiner , Mel Gorman , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 2/5] mm/page_alloc: use smallest fallback page first in movable allocation Message-ID: <20161014012615.GB4993@js1304-P5Q-DELUXE> References: <1476346102-26928-1-git-send-email-iamjoonsoo.kim@lge.com> <1476346102-26928-3-git-send-email-iamjoonsoo.kim@lge.com> <2567dd30-89c7-b9d2-c327-5dec8c536040@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2567dd30-89c7-b9d2-c327-5dec8c536040@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 Content-Length: 2182 Lines: 50 On Thu, Oct 13, 2016 at 11:12:10AM +0200, Vlastimil Babka wrote: > On 10/13/2016 10:08 AM, js1304@gmail.com wrote: > >From: Joonsoo Kim > > > >When we try to find freepage in fallback buddy list, we always serach > >the largest one. This would help for fragmentation if we process > >unmovable/reclaimable allocation request because it could cause permanent > >fragmentation on movable pageblock and spread out such allocations would > >cause more fragmentation. But, movable allocation request is > >rather different. It would be simply freed or migrated so it doesn't > >contribute to fragmentation on the other pageblock. In this case, it would > >be better not to break the precious highest order freepage so we need to > >search the smallest freepage first. > > I've also pondered this, but then found a lower hanging fruit that > should be hopefully clear win and mitigate most cases of breaking > high-order pages unnecessarily: > > http://marc.info/?l=linux-mm&m=147582914330198&w=2 Yes, I agree with that change. That's the similar patch what I tried before. "mm/page_alloc: don't break highest order freepage if steal" http://marc.info/?l=linux-mm&m=143011930520417&w=2 > > So I would try that first, and then test your patch on top? In your > patch there's a risk that we make it harder for > unmovable/reclaimable pageblocks to become movable again (we start > with the smallest page which means there's lower chance that > move_freepages_block() will convert more than half of the block). Indeed, but, with your "count movable pages when stealing", risk would disappear. :) > And Johannes's report seems to be about a regression in exactly this > aspect of the heuristics. Even if your change slows down the breaking high order freepage, but, it would provide just a small delay to break. High order freepage would be broken soon and we cannot prevent to decrease high order freepage in the system. With my approach, high order freepage would stay longer time. For Johannes case, my approach doesn't aim at recovering from that situation. Instead, it tries to prevent such situation that migratetype of pageblock is changed. Thanks.