From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f54.google.com (mail-pa0-f54.google.com [209.85.220.54]) by kanga.kvack.org (Postfix) with ESMTP id B36B96B007E for ; Thu, 3 Mar 2016 23:32:07 -0500 (EST) Received: by mail-pa0-f54.google.com with SMTP id bj10so27728125pad.2 for ; Thu, 03 Mar 2016 20:32:07 -0800 (PST) Received: from lgeamrelo11.lge.com (LGEAMRELO11.lge.com. [156.147.23.51]) by mx.google.com with ESMTP id e12si2882535pat.167.2016.03.03.20.32.06 for ; Thu, 03 Mar 2016 20:32:06 -0800 (PST) Date: Fri, 4 Mar 2016 13:32:32 +0900 From: Joonsoo Kim Subject: Re: Suspicious error for CMA stress test Message-ID: <20160304043232.GC12036@js1304-P5Q-DELUXE> References: <56D6F008.1050600@huawei.com> <56D79284.3030009@redhat.com> <56D832BD.5080305@huawei.com> <20160304020232.GA12036@js1304-P5Q-DELUXE> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160304020232.GA12036@js1304-P5Q-DELUXE> Sender: owner-linux-mm@kvack.org List-ID: To: Hanjun Guo Cc: 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 , "thunder.leizhen@huawei.com" , dingtinahong , chenjie6@huawei.com, "linux-mm@kvack.org" On Fri, Mar 04, 2016 at 11:02:33AM +0900, Joonsoo Kim wrote: > On Thu, Mar 03, 2016 at 08:49:01PM +0800, Hanjun Guo wrote: > > On 2016/3/3 15:42, Joonsoo Kim wrote: > > > 2016-03-03 10:25 GMT+09:00 Laura Abbott : > > >> (cc -mm and Joonsoo Kim) > > >> > > >> > > >> On 03/02/2016 05:52 AM, Hanjun Guo wrote: > > >>> Hi, > > >>> > > >>> I came across a suspicious error for CMA stress test: > > >>> > > >>> Before the test, I got: > > >>> -bash-4.3# cat /proc/meminfo | grep Cma > > >>> CmaTotal: 204800 kB > > >>> CmaFree: 195044 kB > > >>> > > >>> > > >>> After running the test: > > >>> -bash-4.3# cat /proc/meminfo | grep Cma > > >>> CmaTotal: 204800 kB > > >>> CmaFree: 6602584 kB > > >>> > > >>> So the freed CMA memory is more than total.. > > >>> > > >>> Also the the MemFree is more than mem total: > > >>> > > >>> -bash-4.3# cat /proc/meminfo > > >>> MemTotal: 16342016 kB > > >>> MemFree: 22367268 kB > > >>> MemAvailable: 22370528 kB > > [...] > > >> > > >> I played with this a bit and can see the same problem. The sanity > > >> check of CmaFree < CmaTotal generally triggers in > > >> __move_zone_freepage_state in unset_migratetype_isolate. > > >> This also seems to be present as far back as v4.0 which was the > > >> first version to have the updated accounting from Joonsoo. > > >> Were there known limitations with the new freepage accounting, > > >> Joonsoo? > > > I don't know. I also played with this and looks like there is > > > accounting problem, however, for my case, number of free page is slightly less > > > than total. I will take a look. > > > > > > Hanjun, could you tell me your malloc_size? I tested with 1 and it doesn't > > > look like your case. > > > > I tested with malloc_size with 2M, and it grows much bigger than 1M, also I > > did some other test: > > Thanks! Now, I can re-generate erronous situation you mentioned. > > > > > - run with single thread with 100000 times, everything is fine. > > > > - I hack the cam_alloc() and free as below [1] to see if it's lock issue, with > > the same test with 100 multi-thread, then I got: > > [1] would not be sufficient to close this race. > > Try following things [A]. And, for more accurate test, I changed code a bit more > to prevent kernel page allocation from cma area [B]. This will prevent kernel > page allocation from cma area completely so we can focus cma_alloc/release race. > > Although, this is not correct fix, it could help that we can guess > where the problem is. More correct fix is something like below. Please test it. It checks problematic buddy merging and prevent it. I will try to find another way that is less intrusive for freepath performance. Thanks. ---------------->8-----------------------