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Mon, 02 Aug 2021 06:32:17 -0700 (PDT) X-Google-Smtp-Source: ABdhPJwGIz1xoKvPOqISRjUd4eV/HXaGubjZfpkkJ13bdLQELNFSuifXslmT7Q3i7tSI+D+KXlK5Dg== X-Received: by 2002:ac8:4f11:: with SMTP id b17mr14083609qte.33.1627911137439; Mon, 02 Aug 2021 06:32:17 -0700 (PDT) Received: from llong.remote.csb ([2601:191:8500:76c0::cdbc]) by smtp.gmail.com with ESMTPSA id 2sm2507742qtz.1.2021.08.02.06.32.16 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 02 Aug 2021 06:32:16 -0700 (PDT) From: Waiman Long X-Google-Original-From: Waiman Long Subject: Re: [PATCH] mm/memcg: Fix incorrect flushing of lruvec data in obj_stock To: Michal Hocko Cc: Johannes Weiner , Vladimir Davydov , Andrew Morton , Tejun Heo , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Vlastimil Babka , Roman Gushchin , linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org, Shakeel Butt , Muchun Song , Alex Shi , Chris Down , Yafang Shao , Wei Yang , Masayoshi Mizuma , Xing Zhengjun , Matthew Wilcox References: <20210802022827.10192-1-longman@redhat.com> Message-ID: <771539d4-765c-05c7-ab19-d4cae3d29efd@redhat.com> Date: Mon, 2 Aug 2021 09:32:16 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Authentication-Results: imf21.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=IcaoBjbQ; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=KCIbmU01; spf=none (imf21.hostedemail.com: domain of llong@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=llong@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: C2495D009345 X-Stat-Signature: a5jhhg3pcf1ef4dgn9aguuidp6rcxnah X-HE-Tag: 1627911142-62048 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 8/2/21 2:28 AM, Michal Hocko wrote: > On Sun 01-08-21 22:28:27, Waiman Long wrote: >> When mod_objcg_state() is called with a pgdat that is different from >> that in the obj_stock, the old lruvec data cached in obj_stock are >> flushed out. Unfortunately, they were flushed to the new pgdat and >> hence the wrong node, not the one cached in obj_stock. > It would be great to explicitly mention user observable problems here. I > do assume this will make slab stats skewed but the effect wouldn't be > very big, right? It is the /sys/devices/system/node/node*/meminfo that will get skewed. Not /proc/meminfo. So it is a relatively minor issue. Will update the patch to mention that. >> Fix that by flushing the data to the cached pgdat instead. >> >> Fixes: 68ac5b3c8db2 ("mm/memcg: cache vmstat data in percpu memcg_stock_pcp") >> Signed-off-by: Waiman Long > Acked-by: Michal Hocko > >> --- >> mm/memcontrol.c | 8 +++++--- >> 1 file changed, 5 insertions(+), 3 deletions(-) >> >> diff --git a/mm/memcontrol.c b/mm/memcontrol.c >> index ae1f5d0cb581..881ec4ddddcd 100644 >> --- a/mm/memcontrol.c >> +++ b/mm/memcontrol.c >> @@ -3106,17 +3106,19 @@ void mod_objcg_state(struct obj_cgroup *objcg, struct pglist_data *pgdat, >> stock->cached_pgdat = pgdat; >> } else if (stock->cached_pgdat != pgdat) { >> /* Flush the existing cached vmstat data */ >> + struct pglist_data *oldpg = stock->cached_pgdat; >> + >> + stock->cached_pgdat = pgdat; >> if (stock->nr_slab_reclaimable_b) { >> - mod_objcg_mlstate(objcg, pgdat, NR_SLAB_RECLAIMABLE_B, >> + mod_objcg_mlstate(objcg, oldpg, NR_SLAB_RECLAIMABLE_B, >> stock->nr_slab_reclaimable_b); >> stock->nr_slab_reclaimable_b = 0; >> } >> if (stock->nr_slab_unreclaimable_b) { >> - mod_objcg_mlstate(objcg, pgdat, NR_SLAB_UNRECLAIMABLE_B, >> + mod_objcg_mlstate(objcg, oldpg, NR_SLAB_UNRECLAIMABLE_B, >> stock->nr_slab_unreclaimable_b); >> stock->nr_slab_unreclaimable_b = 0; >> } >> - stock->cached_pgdat = pgdat; > Minor nit. Is there any reason to move the cached_pgdat? TBH I found the > original way better from the readability POV. Right. Will move it back to its original place. Cheers, Longman