Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756188AbcCRU6n (ORCPT ); Fri, 18 Mar 2016 16:58:43 -0400 Received: from mx2.suse.de ([195.135.220.15]:52894 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751546AbcCRU6k (ORCPT ); Fri, 18 Mar 2016 16:58:40 -0400 Subject: Re: Suspicious error for CMA stress test To: Lucas Stach References: <56DD38E7.3050107@huawei.com> <56DDCB86.4030709@redhat.com> <56DE30CB.7020207@huawei.com> <56DF7B28.9060108@huawei.com> <56E2FB5C.1040602@suse.cz> <20160314064925.GA27587@js1304-P5Q-DELUXE> <56E662E8.700@suse.cz> <20160314071803.GA28094@js1304-P5Q-DELUXE> <56E92AFC.9050208@huawei.com> <20160317065426.GA10315@js1304-P5Q-DELUXE> <56EA77BC.2090702@huawei.com> <56EAD0B4.2060807@suse.cz> <56EC0C41.70503@suse.cz> <1458312126.18134.45.camel@pengutronix.de> Cc: Joonsoo Kim , Hanjun Guo , Joonsoo Kim , "Leizhen (ThunderTown)" , Laura Abbott , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , Andrew Morton , Sasha Levin , Laura Abbott , qiuxishi , Catalin Marinas , Will Deacon , Arnd Bergmann , dingtinahong , chenjie6@huawei.com, "linux-mm@kvack.org" From: Vlastimil Babka Message-ID: <56EC6BFB.2020107@suse.cz> Date: Fri, 18 Mar 2016 21:58:35 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 MIME-Version: 1.0 In-Reply-To: <1458312126.18134.45.camel@pengutronix.de> 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: 2362 Lines: 45 On 03/18/2016 03:42 PM, Lucas Stach wrote: > Am Freitag, den 18.03.2016, 15:10 +0100 schrieb Vlastimil Babka: >> On 03/17/2016 04:52 PM, Joonsoo Kim wrote: >> > 2016-03-18 0:43 GMT+09:00 Vlastimil Babka : >> >> OK, here it is. Hanjun can you please retest this, as I'm not sure if you had >> the same code due to the followup one-liner patches in the thread. Lucas, see if >> it helps with your issue as well. Laura and Joonsoo, please also test and review >> and check changelog if my perception of the problem is accurate :) >> > > This doesn't help for my case, as it is still trying to merge pages in > isolated ranges. It even tries extra hard at doing so. > > With concurrent isolation and frees going on this may lead to the start > page of the range to be isolated merging into an higher order buddy page > if it isn't already pageblock aligned, leading both test_pages_isolated > and isolate_freepages to fail on an otherwise perfectly fine range. > > What I am arguing is that if a page is freed into an isolated range we > should not try merge it with it's buddies at all, by setting max_order = > order. If the range is isolated because want to isolate freepages from > it, the work to do the merging is wasted, as isolate_freepages will > split higher order pages into order-0 pages again. > > If we already finished isolating freepages and are in the process of > undoing the isolation, we don't strictly need to do the merging in > __free_one_page, but can defer it to unset_migratetype_isolate, allowing > to simplify those code paths by disallowing any merging of isolated > pages at all. Oh, I think understand now. Yeah, skipping merging for pages in isolated pageblocks might be a rather elegant solution. But still, we would have to check buddy's migratetype at order >= pageblock_order like my patch does, which is annoying. Because even without isolated merging, the buddy might have already had order>=pageblock_order when it was isolated. So what if isolation also split existing buddies in the pageblock immediately when it sets the MIGRATETYPE_ISOLATE on the pageblock? Then we would have it guaranteed that there's no isolated buddy - a buddy candidate at order >= pageblock_order either has a smaller order (so it's not a buddy) or is not MIGRATE_ISOLATE so it's safe to merge with. Does that make sense?