From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf0-f52.google.com (mail-lf0-f52.google.com [209.85.215.52]) by kanga.kvack.org (Postfix) with ESMTP id 841836B0009 for ; Mon, 1 Feb 2016 20:06:36 -0500 (EST) Received: by mail-lf0-f52.google.com with SMTP id m1so33376409lfg.0 for ; Mon, 01 Feb 2016 17:06:36 -0800 (PST) Received: from szxga01-in.huawei.com (szxga01-in.huawei.com. [58.251.152.64]) by mx.google.com with ESMTPS id ml3si15192895lbc.61.2016.02.01.17.06.28 for (version=TLS1 cipher=AES128-SHA bits=128/128); Mon, 01 Feb 2016 17:06:34 -0800 (PST) Message-ID: <56B00004.1070706@huawei.com> Date: Tue, 2 Feb 2016 09:01:56 +0800 From: Xishi Qiu MIME-Version: 1.0 Subject: Re: [RFC PATCH 0/2] avoid external fragmentation related to migration fallback References: <56ABD3B8.3080306@suse.cz> <20160201135351.GB8337@techsingularity.net> In-Reply-To: <20160201135351.GB8337@techsingularity.net> Content-Type: text/plain; charset="ISO-8859-15" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Mel Gorman Cc: Vlastimil Babka , ChengYi He , Andrew Morton , Michal Hocko , David Rientjes , Joonsoo Kim , Yaowei Bai , Alexander Duyck , "'Kirill A . Shutemov'" , Johannes Weiner , linux-mm@kvack.org, linux-kernel@vger.kernel.org On 2016/2/1 21:53, Mel Gorman wrote: > On Fri, Jan 29, 2016 at 10:03:52PM +0100, Vlastimil Babka wrote: >>> Since the root cause is that fallbacks might frequently split order-2 >>> and order-3 pages of the other migration types. This patch tweaks >>> fallback mechanism to avoid splitting order-2 and order-3 pages. while >>> fallbacks happen, if the largest feasible pages are less than or queal to >>> COSTLY_ORDER, i.e. 3, then try to select the smallest feasible pages. The >>> reason why fallbacks prefer the largest feasiable pages is to increase >>> fallback efficiency since fallbacks are likely to happen again. By >>> stealing the largest feasible pages, it could reduce the oppourtunities >>> of antoher fallback. Besides, it could make consecutive allocations more >>> approximate to each other and make system less fragment. However, if the >>> largest feasible pages are less than or equal to order-3, fallbacks might >>> split it and make the upcoming order-3 page allocations fail. >> >> In theory I don't see immediately why preferring smaller pages for >> fallback should be a clear win. If it's Unmovable allocations stealing >> from Movable pageblocks, the allocations will spread over larger areas >> instead of being grouped together. Maybe, for Movable allocations >> stealing from Unmovable allocations, preferring smallest might make >> sense and be safe, as any extra fragmentation is fixable bycompaction. > > I strongly agree that spreading the fallback allocations over a larger > area is likely to have a negative impact. Given the age of the kernel > being tested, it would make sense to either rebase or at the very last > backport the patches that affect watermark calculations and the > treatment of high-order pages. > Is it the feature of MIGRATE_HIGHATOMIC? Thanks, Xishi Qiu -- 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