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[195.135.220.15]) by mx.google.com with ESMTPS id c9si2250155eds.357.2019.04.19.05.54.47 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 19 Apr 2019 05:54:47 -0700 (PDT) Received-SPF: pass (google.com: domain of vbabka@suse.cz designates 195.135.220.15 as permitted sender) client-ip=195.135.220.15; Authentication-Results: mx.google.com; spf=pass (google.com: domain of vbabka@suse.cz designates 195.135.220.15 as permitted sender) smtp.mailfrom=vbabka@suse.cz X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 73BB6AB7D; Fri, 19 Apr 2019 12:54:46 +0000 (UTC) Subject: Re: v5.1-rc5 s390x WARNING To: Mel Gorman Cc: Li Wang , Minchan Kim , linux-mm References: <73fbe83d-97d8-c05f-38fa-5e1a0eec3c10@suse.cz> <20190418135452.GF18914@techsingularity.net> From: Vlastimil Babka Openpgp: preference=signencrypt Autocrypt: addr=vbabka@suse.cz; prefer-encrypt=mutual; keydata= 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hFNGBTYyPq6mGW9jqaQ8en3ZmmJyw3CHwxZ5FZQ5qc55xgshKiy8jEtxh+dgB9d8zE/S/UGI E99N/q+kEKSgSMQMJ/CYPHQJVTi4YHh1yq/qTkHRX+ortrF5VEeDJDv+SljNStIxUdroPD29 2ijoaMFTAU+uBtE14UP5F+LWdmRdEGS1Ah1NwooL27uAFllTDQxDhg/+LJ/TqB8ZuidOIy1B xVKRSg3I2m+DUTVqBy7Lixo73hnW69kSjtqCeamY/NSu6LNP+b0wAOKhwz9hBEwEHLp05+mj 5ZFJyfGsOiNUcMoO/17FO4EBxSDP3FDLllpuzlFD7SXkfJaMWYmXIlO0jLzdfwfcnDzBbPwO hBM8hvtsyq8lq8vJOxv6XD6xcTtj5Az8t2JjdUX6SF9hxJpwhBU0wrCoGDkWp4Bbv6jnF7zP Nzftr4l8RuJoywDIiJpdaNpSlXKpj/K6KrnyAI/joYc7 Message-ID: Date: Fri, 19 Apr 2019 14:51:26 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20190418135452.GF18914@techsingularity.net> Content-Type: text/plain; charset=iso-8859-15 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 4/18/19 3:54 PM, Mel Gorman wrote: > On Wed, Apr 17, 2019 at 10:54:38AM +0200, Vlastimil Babka wrote: >> On 4/17/19 10:35 AM, Li Wang wrote: >>> Hi there, >>> >>> I catched this warning on v5.1-rc5(s390x). It was trggiered in fork & malloc & memset stress test, but the reproduced rate is very low. I'm working on find a stable reproducer for it. >>> >>> Anyone can have a look first? >>> >>> [ 1422.124060] WARNING: CPU: 0 PID: 9783 at mm/page_alloc.c:3777 __alloc_pages_irect_compact+0x182/0x190 >> >> This means compaction was either skipped or deferred, yet it captured a >> page. We have some registers with value 1 and 2, which is >> COMPACT_SKIPPED and COMPACT_DEFERRED, so it could be one of those. >> Probably COMPACT_SKIPPED. I think a race is possible: >> >> - compact_zone_order() sets up current->capture_control >> - compact_zone() calls compaction_suitable() which returns >> COMPACT_SKIPPED, so it also returns >> - interrupt comes and its processing happens to free a page that forms >> high-order page, since 'current' isn't changed during interrupt (IIRC?) >> the capture_control is still active and the page is captured >> - compact_zone_order() does *capture = capc.page >> >> What do you think, Mel, does it look plausible? > > It's plausible, just extremely unlikely. I think the most likely result > was that a page filled the per-cpu lists and a bunch of pages got freed > in a batch from interrupt context. Sure, good point. Per-cpu lists make the scenario even more rare, but once it's full, there's a higher change the batch free from the interrupt will result in high-order page being formed. >> Not sure whether we want >> to try avoiding this scenario, or just remove the warning and be >> grateful for the successful capture :) >> > > Avoiding the scenario is pointless because it's not wrong. The check was > initially meant to catch serious programming errors such as using a > stale page pointer so I think the right patch is below. Li Wang, how > reproducible is this and would you be willing to test it? > > ---8<--- > mm, page_alloc: Always use a captured page regardless of compaction result > > During the development of commit 5e1f0f098b46 ("mm, compaction: capture > a page under direct compaction"), a paranoid check was added to ensure > that if a captured page was available after compaction that it was > consistent with the final state of compaction. The intent was to catch > serious programming bugs such as using a stale page pointer and causing > corruption problems. > > However, it is possible to get a captured page even if compaction was > unsuccessful if an interrupt triggered and happened to free pages in > interrupt context that got merged into a suitable high-order page. It's > highly unlikely but Li Wang did report the following warning on s390 > > [ 1422.124060] WARNING: CPU: 0 PID: 9783 at mm/page_alloc.c:3777 __alloc_pages_irect_compact+0x182/0x190 > [ 1422.124065] Modules linked in: rpcsec_gss_krb5 auth_rpcgss nfsv4 dns_resolver > nfs lockd grace fscache sunrpc pkey ghash_s390 prng xts aes_s390 des_s390 > des_generic sha512_s390 zcrypt_cex4 zcrypt vmur binfmt_misc ip_tables xfs > libcrc32c dasd_fba_mod qeth_l2 dasd_eckd_mod dasd_mod qeth qdio lcs ctcm > ccwgroup fsm dm_mirror dm_region_hash dm_log dm_mod > [ 1422.124086] CPU: 0 PID: 9783 Comm: copy.sh Kdump: loaded Not tainted 5.1.0-rc 5 #1 > > This patch simply removes the check entirely instead of trying to be > clever about pages freed from interrupt context. If a serious programming > error was introduced, it is highly likely to be caught by prep_new_page() > instead. > > Fixes: 5e1f0f098b46 ("mm, compaction: capture a page under direct compaction") > Reported-by: Li Wang > Signed-off-by: Mel Gorman Yup, no need for a Cc: stable on a very rare WARN_ON_ONCE. So the AI will pick it anyway... Acked-by: Vlastimil Babka > --- > mm/page_alloc.c | 5 ----- > 1 file changed, 5 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index d96ca5bc555b..cfaba3889fa2 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -3773,11 +3773,6 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order, > memalloc_noreclaim_restore(noreclaim_flag); > psi_memstall_leave(&pflags); > > - if (*compact_result <= COMPACT_INACTIVE) { > - WARN_ON_ONCE(page); > - return NULL; > - } > - > /* > * At least in one zone compaction wasn't deferred or skipped, so let's > * count a compaction stall >