From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io0-f182.google.com (mail-io0-f182.google.com [209.85.223.182]) by kanga.kvack.org (Postfix) with ESMTP id 34A316B007E for ; Wed, 23 Mar 2016 00:42:35 -0400 (EDT) Received: by mail-io0-f182.google.com with SMTP id c63so16144030iof.0 for ; Tue, 22 Mar 2016 21:42:35 -0700 (PDT) Received: from lgeamrelo13.lge.com (LGEAMRELO13.lge.com. [156.147.23.53]) by mx.google.com with ESMTP id 64si1533028ioz.0.2016.03.22.21.42.33 for ; Tue, 22 Mar 2016 21:42:34 -0700 (PDT) Date: Wed, 23 Mar 2016 13:44:07 +0900 From: Joonsoo Kim Subject: Re: Suspicious error for CMA stress test Message-ID: <20160323044407.GB4624@js1304-P5Q-DELUXE> References: <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <56EC0C41.70503@suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Vlastimil Babka Cc: Hanjun Guo , "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" , Lucas Stach On Fri, Mar 18, 2016 at 03:10:09PM +0100, Vlastimil Babka wrote: > On 03/17/2016 04:52 PM, Joonsoo Kim wrote: > > 2016-03-18 0:43 GMT+09:00 Vlastimil Babka : > >>>>>> > >>>>>> Okay. I used following slightly optimized version and I need to > >>>>>> add 'max_order = min_t(unsigned int, MAX_ORDER, pageblock_order + 1)' > >>>>>> to yours. Please consider it, too. > >>>>> > >>>>> Hmm, this one is not work, I still can see the bug is there after > >>>>> applying > >>>>> this patch, did I miss something? > >>>> > >>>> I may find that there is a bug which was introduced by me some time > >>>> ago. Could you test following change in __free_one_page() on top of > >>>> Vlastimil's patch? > >>>> > >>>> -page_idx = pfn & ((1 << max_order) - 1); > >>>> +page_idx = pfn & ((1 << MAX_ORDER) - 1); > >>> > >>> > >>> I tested Vlastimil's patch + your change with stress for more than half > >>> hour, the bug > >>> I reported is gone :) > >> > >> > >> Oh, ok, will try to send proper patch, once I figure out what to write in > >> the changelog :) > > > > Thanks in advance! > > > > 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 :) > > Thanks > > ----8<---- > From: Vlastimil Babka > Date: Fri, 18 Mar 2016 14:22:31 +0100 > Subject: [PATCH] mm/page_alloc: prevent merging between isolated and other > pageblocks > > Hanjun Guo has reported that a CMA stress test causes broken accounting of > CMA and free pages: > > > 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 > > Laura Abbott has confirmed the issue and suspected the freepage accounting > rewrite around 3.18/4.0 by Joonsoo Kim. Joonsoo had a theory that this is > caused by unexpected merging between MIGRATE_ISOLATE and MIGRATE_CMA > pageblocks: > > > CMA isolates MAX_ORDER aligned blocks, but, during the process, > > partialy isolated block exists. If MAX_ORDER is 11 and > > pageblock_order is 9, two pageblocks make up MAX_ORDER > > aligned block and I can think following scenario because pageblock > > (un)isolation would be done one by one. > > > > (each character means one pageblock. 'C', 'I' means MIGRATE_CMA, > > MIGRATE_ISOLATE, respectively. > > > > CC -> IC -> II (Isolation) > > II -> CI -> CC (Un-isolation) > > > > If some pages are freed at this intermediate state such as IC or CI, > > that page could be merged to the other page that is resident on > > different type of pageblock and it will cause wrong freepage count. > > This was supposed to be prevented by CMA operating on MAX_ORDER blocks, but > since it doesn't hold the zone->lock between pageblocks, a race window does > exist. > > It's also likely that unexpected merging can occur between MIGRATE_ISOLATE > and non-CMA pageblocks. This should be prevented in __free_one_page() since > commit 3c605096d315 ("mm/page_alloc: restrict max order of merging on isolated > pageblock"). However, we only check the migratetype of the pageblock where > buddy merging has been initiated, not the migratetype of the buddy pageblock > (or group of pageblocks) which can be MIGRATE_ISOLATE. > > Joonsoo has suggested checking for buddy migratetype as part of > page_is_buddy(), but that would add extra checks in allocator hotpath and > bloat-o-meter has shown significant code bloat (the function is inline). > > This patch reduces the bloat at some expense of more complicated code. The > buddy-merging while-loop in __free_one_page() is initially bounded to > pageblock_border and without any migratetype checks. The checks are placed > outside, bumping the max_order if merging is allowed, and returning to the > while-loop with a statement which can't be possibly considered harmful. > > This fixes the accounting bug and also removes the arguably weird state in the > original commit 3c605096d315 where buddies could be left unmerged. > > Fixes: 3c605096d315 ("mm/page_alloc: restrict max order of merging on isolated pageblock") > Link: https://lkml.org/lkml/2016/3/2/280 > Reported-by: Hanjun Guo > Debugged-by: Laura Abbott > Debugged-by: Joonsoo Kim > Signed-off-by: Vlastimil Babka > Cc: # 3.18+ > --- > mm/page_alloc.c | 46 +++++++++++++++++++++++++++++++++------------- > 1 file changed, 33 insertions(+), 13 deletions(-) Acked-by: Joonsoo Kim Thanks for taking care of this issue!. Thanks. -- 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