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[109.81.31.109]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-6411f86e12fsm14093400a12.34.2025.11.11.13.01.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 11 Nov 2025 13:01:38 -0800 (PST) Date: Tue, 11 Nov 2025 22:01:37 +0100 From: Michal Hocko To: Waiman Long Cc: Leon Huang Fu , linux-mm@kvack.org, tj@kernel.org, mkoutny@suse.com, hannes@cmpxchg.org, roman.gushchin@linux.dev, shakeel.butt@linux.dev, muchun.song@linux.dev, akpm@linux-foundation.org, joel.granados@kernel.org, jack@suse.cz, laoar.shao@gmail.com, mclapinski@google.com, kyle.meyer@hpe.com, corbet@lwn.net, lance.yang@linux.dev, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org Subject: Re: [PATCH mm-new v3] mm/memcontrol: Add memory.stat_refresh for on-demand stats flushing Message-ID: References: <20251110101948.19277-1-leon.huangfu@shopee.com> <9a9a2ede-af6e-413a-97a0-800993072b22@redhat.com> <061cdd9e-a70b-4d45-909a-6d50f4da8ef3@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <061cdd9e-a70b-4d45-909a-6d50f4da8ef3@redhat.com> X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: BE9674000C X-Stat-Signature: 5zmy7pjzsmbpdn1d17jh5cudexqid5h6 X-Rspam-User: X-HE-Tag: 1762894900-507949 X-HE-Meta: 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 hqapcUL+ On97YFkJIyHZLb2GqqN3amzpfEXSLJYttz76RfoESexmA2rLS/Hsg5JbSXlI0e3Gi6aEUVunZEXQ6WEOwhAK9wT3yJubrP2YzDlqqdyHyRsulUkqUM6x0vkYsD92I5RmxUxIX9Z6SMYUj8Q16xNiHsrbXRVH6QOyKE6SWhrxO/XAkE335RmJVuHZwvV3TXeIXG4BNgD7fd86NeVqfK9nzsewZeDE0kcZ25/Dbu8CuDMQ/O593/UlYy9UIovMtHpXsNhk9X6M1kLDjqvOxuUjX699YU+abQ/El3STJxbwYA8j+eofKG0ujluZ1c1dSYV9o5xlZXo6TVW2npgjPYm0aX129xwYd0aJYSJVWPNNu9ougs4e7nBMHDjZ73RKxhZ21mboXI4Nxi/Nq7+iQfRA995ywQz0XwMV9eBYdutdyHiMUO0eJJgPnyDtkjSdjIsWjSRezJ7DgOpx03veSSXAR1xqLawWPgSWNV6af 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 Tue 11-11-25 15:44:07, Waiman Long wrote: > > On 11/11/25 2:47 PM, Michal Hocko wrote: > > On Tue 11-11-25 14:10:28, Waiman Long wrote: > > [...] > > > > +static void memcg_flush_stats(struct mem_cgroup *memcg, bool force) > > > > +{ > > > > + if (mem_cgroup_disabled()) > > > > + return; > > > > + > > > > + memcg = memcg ?: root_mem_cgroup; > > > > + __mem_cgroup_flush_stats(memcg, force); > > > > +} > > > Shouldn't we impose a limit in term of how frequently this > > > memcg_flush_stats() function can be called like at most a few times per > > This effectivelly invalidates the primary purpose of the interface to > > provide a method to get as-fresh-as-possible value AFAICS. > > > > > second to prevent abuse from user space as stat flushing is expensive? We > > > should prevent some kind of user space DoS attack by using this new API if > > > we decide to implement it. > > What exactly would be an attack vector? > > just repeatedly write a string to the new cgroup file. It will then call > css_rstat_flush() repeatedly. It is not a real DoS attack, but it can still > consume a lot of cpu time and slow down other tasks. How does that differ from writing a limit that would cause a constant memory reclaim from a worklad that you craft and cause a constant CPU activity and even worse lock contention? I guess the answer is that you do not let untrusted entities to create cgroup hierarchies and allow to modify or generally have a write access to control files. Or am I missing something? -- Michal Hocko SUSE Labs