From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f53.google.com (mail-wm0-f53.google.com [74.125.82.53]) by kanga.kvack.org (Postfix) with ESMTP id 43EEC6B025E for ; Tue, 22 Mar 2016 10:47:47 -0400 (EDT) Received: by mail-wm0-f53.google.com with SMTP id l68so167215657wml.1 for ; Tue, 22 Mar 2016 07:47:47 -0700 (PDT) Received: from metis.ext.pengutronix.de (metis.ext.pengutronix.de. [2001:67c:670:201:290:27ff:fe1d:cc33]) by mx.google.com with ESMTPS id r3si37800384wjy.50.2016.03.22.07.47.45 for (version=TLS1_2 cipher=AES128-SHA bits=128/128); Tue, 22 Mar 2016 07:47:45 -0700 (PDT) Message-ID: <1458658023.2171.16.camel@pengutronix.de> Subject: Re: Suspicious error for CMA stress test From: Lucas Stach Date: Tue, 22 Mar 2016 15:47:03 +0100 In-Reply-To: <56EC6BFB.2020107@suse.cz> 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> <56EC6BFB.2020107@suse.cz> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Vlastimil Babka 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" Am Freitag, den 18.03.2016, 21:58 +0100 schrieb Vlastimil Babka: > 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? > This might increase the the overhead of isolation a lot. CMA is also used for small order allocations, so the work of splitting a whole pageblock to allocate a small number of pages out just to merge a lot of them again on unisolation might make this unattractive. My feeling is that checking the buddy migratetype for >=pageblock_order frees might be lower overhead, but I have no hard numbers to back this claim. Then on the other hand moving the work to isolation/unisolation affects only code paths that are expected to be quite slow anyways, doing the check in _free_one_page will affect everyone. Regards, Lucas -- 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