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h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Dph8UJduGjbCAOusaVKDWVM0Nbup/WEtW2XPVYZyxABS6fnmFsoMr73WpsXRlussQ HxY2rKJit6AUd3+Osf46yikDJKhoOHijn52a49QXH1e9jJEph4b5+zVKg0QsAfKqPL RHEp+t/rxhvcm/EDfDvWIWH0yMtLyIW/lra9m5iQ= Date: Sun, 7 Sep 2025 15:10:03 +0200 From: Greg KH To: Andrew Guerrero Cc: cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, hannes@cmpxchg.org, mhocko@kernel.org, vdavydov.dev@gmail.com, akpm@linux-foundation.org, shakeelb@google.com, guro@fb.com, gunnarku@amazon.com, stable@vger.kernel.org Subject: Re: [PATCH] mm: memcontrol: fix memcg accounting during cpu hotplug Message-ID: <2025090735-glade-paralegal-cdd1@gregkh> References: <20250906032108.30539-1-ajgja@amazon.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250906032108.30539-1-ajgja@amazon.com> X-Stat-Signature: hzgpwpjk1ot45i8mzt3ohofrnroaimhp X-Rspam-User: X-Rspamd-Queue-Id: ACDA1180016 X-Rspamd-Server: rspam05 X-HE-Tag: 1757250607-210732 X-HE-Meta: U2FsdGVkX1+ifzHvfeaDlg1LpPxiOeQgttaFb/0uUor02DH3wIoxAVflYwhKgMQTLAcJX01bsSZ8Ahfu/1OLEA2kgiuBu962gPkgGX2BTWqGG54qkfw83LN04GRwA+KYdoWXl1UXbufvYRrXGtFDPb1amh87gRwIuEfEegIQhEyOYRt5c0bJk4V9zAVm3hbjGHMcaCf8bCdRLBxVVwI66GJoLuQizNdbYj0GulAWQy8rb1TYL26EpASzAjMhWB4Fjx3tpJt4NAuyDrvJBd8az+qK7wvCG3fg+Lka4VNUtXbKr1qQBaEbb/Al8q/B8OeuKxCfBHGbJNzi5MYMqTQSZZWB+NBA3kiM5WOnsocsCFU1iDQimxCW2txnaS7OVkF/drLygfdqhyooU8tzBmuCE7gnUopPbp62QUsIXU8n+LeJPIYNtVzzeXzRxXLsIlHrCIpQULT3mAdWGYRoyFQQnwm4Phlq84sdoPARG9wolNgsx4QRWP0mk1N5BGr7psP4/605kBUVoymi/+hKstn8NSxoO2YewpngexlYkjIvT/M0MKPuav+KdBvfF72TYP02petDXUDKhOuwCWmlWM9AoJ3Lxd8YjggOkgE8OM7GS7LYtadEo6TfgSmu3xl2ZuIEdOSWJaExGyTuWh97KkWtc6Llu7FJUGac/Y9JJ8EPvWmI7/yZ42EBsV6dDZ3TGZj/T7nm+sNMjCLMULOuAxoDGwv18H4H0U4OEnbZK4R83ZomwBAt8ipwH9atB+f6bEUDk2VXjOYX3/h6eqQqgEdNW8w0w+ZxaXzFhscp9SQCB9l2YL8I7QEaU6hJExnNNQF0qnNezReV7MbMUopmB8hxpI4oDUTk2AQGPLZj4CFx6vpzWlfNtpc8ZqeoFu8jPh5ATv4dd8MAxzaKskyDrr3Y1KRBmanI1SsWV3VMca3SFuZeJniDv6DtuokqVIN/+NjPW8CxGbl2zETEWj9Rj9r HKUxj8MO EnhZsgW2g4Oh/H/WbwmdoIOZaG3l/9XQ0Fz0KLMmUzWgxNvI5Y3rX4Op2ccqTsU0gl00ONxwvlr9TFYrBWsaOVCzXsXkE9j9t/zjEvnWsJzG87cRWzfAktvEnXZVleHkQKTt2RyfNMN1Jf0uMLi4ndPQb1sRwyX+XnX2luhnRMmD3eQMznqWqQ97naf9b8jYof/bQ6dou1KKNWxvDJ49Be5/f62/infdLsiMO0hoS6VyVeQN6tI1iiv/p6pm8rIU7czArMU/+mBFvg1cY3JhF6bNE0jHy90ytsoL6CpCTGP3jVUQdcJwoKHGJr9FFdsdpTD5Fu/Ascbu9i2HNrNVVW5HUOjLkVkBOZx/7ahOAs//RXi5BVO7QFYVhmP0wIyDUy9s/Ht2/j48uZBOtk6vavX3JFYR2b5rBjNBW 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: List-Subscribe: List-Unsubscribe: On Sat, Sep 06, 2025 at 03:21:08AM +0000, Andrew Guerrero wrote: > A filesystem writeback performance issue was discovered by repeatedly > running CPU hotplug operations while a process in a cgroup with memory > and io controllers enabled wrote to an ext4 file in a loop. > > When a CPU is offlined, the memcg_hotplug_cpu_dead() callback function > flushes per-cpu vmstats counters. However, instead of applying a per-cpu > counter once to each cgroup in the heirarchy, the per-cpu counter is > applied repeatedly just to the nested cgroup. Under certain conditions, > the per-cpu NR_FILE_DIRTY counter is routinely positive during hotplug > events and the dirty file count artifically inflates. Once the dirty > file count grows past the dirty_freerun_ceiling(), balance_dirty_pages() > starts a backgroup writeback each time a file page is marked dirty > within the nested cgroup. > > This change fixes memcg_hotplug_cpu_dead() so that the per-cpu vmstats > and vmevents counters are applied once to each cgroup in the heirarchy, > similar to __mod_memcg_state() and __count_memcg_events(). > > Fixes: 42a300353577 ("mm: memcontrol: fix recursive statistics correctness & scalabilty") > Signed-off-by: Andrew Guerrero > Reviewed-by: Gunnar Kudrjavets > --- > Hey all, > > This patch is intended for the 5.10 longterm release branch. It will not apply > cleanly to mainline and is inadvertantly fixed by a larger series of changes in > later release branches: > a3d4c05a4474 ("mm: memcontrol: fix cpuhotplug statistics flushing"). Why can't we take those instead? > In 5.15, the counter flushing code is completely removed. This may be another > viable option here too, though it's a larger change. If it's not needed anymore, why not just remove it with the upstream commits as well? thanks, greg k-h