Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754278AbcJMLF0 (ORCPT ); Thu, 13 Oct 2016 07:05:26 -0400 Received: from mx2.suse.de ([195.135.220.15]:51816 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754208AbcJMLFP (ORCPT ); Thu, 13 Oct 2016 07:05:15 -0400 Subject: Re: [RFC PATCH 5/5] mm/page_alloc: support fixed migratetype pageblock To: js1304@gmail.com, Andrew Morton References: <1476346102-26928-1-git-send-email-iamjoonsoo.kim@lge.com> <1476346102-26928-6-git-send-email-iamjoonsoo.kim@lge.com> Cc: Johannes Weiner , Mel Gorman , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Joonsoo Kim From: Vlastimil Babka Message-ID: Date: Thu, 13 Oct 2016 13:05:11 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.3.0 MIME-Version: 1.0 In-Reply-To: <1476346102-26928-6-git-send-email-iamjoonsoo.kim@lge.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2292 Lines: 44 On 10/13/2016 10:08 AM, js1304@gmail.com wrote: > From: Joonsoo Kim > > We have migratetype facility to minimise fragmentation. It dynamically > changes migratetype of pageblock based on some criterias but it never > be perfect. Some migratetype pages are often placed in the other > migratetype pageblock. We call this pageblock as mixed pageblock. > > There are two types of mixed pageblock. Movable page on unmovable > pageblock and unmovable page on movable pageblock. (I simply ignore > reclaimble migratetype/pageblock for easy explanation.) Earlier case is > not a big problem because movable page is reclaimable or migratable. We can > reclaim/migrate it when necessary so it usually doesn't contribute > fragmentation. Actual problem is caused by later case. We don't have > any way to reclaim/migrate this page and it prevents to make high order > freepage. > > This later case happens when there is too less unmovable freepage. When > unmovable freepage runs out, fallback allocation happens and unmovable > allocation would be served by movable pageblock. > > To solve/prevent this problem, we need to have enough unmovable freepage > to satisfy all unmovable allocation request by unmovable pageblock. > If we set enough unmovable pageblock at boot and fix it's migratetype > until power off, we would have more unmovable freepage during runtime and > mitigate above problem. > > This patch provides a way to set minimum number of unmovable pageblock > at boot time. In my test, with proper setup, I can't see any mixed > pageblock where unmovable allocation stay on movable pageblock. So if I get this correctly, the fixed-as-unmovable bit doesn't actually prevent fallbacks to such pageblocks? Then I'm surprised that's enough to make any difference. Also Johannes's problem is that there are too many unmovable pageblocks, so I'm a bit skeptical that simply preallocating some will help his workload. But we'll see... In any case I wouldn't pursue a solution that requires user configuration, until as a last resort. Hopefully we can make the heuristics good enough so that's not necessary. Sorry for my mostly negative feedback to your series, I'm glad you pursuit this as well, and hope we'll eventually find a good solution :) Vlastimil