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[109.81.31.109]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-b72bf9bdf15sm1411961966b.62.2025.11.11.11.48.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 11 Nov 2025 11:48:05 -0800 (PST) Date: Tue, 11 Nov 2025 20:47:59 +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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <9a9a2ede-af6e-413a-97a0-800993072b22@redhat.com> X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 48A8640009 X-Stat-Signature: to8ysxp61rfisn75pst4kk4tedfi95kk X-Rspam-User: X-HE-Tag: 1762890487-360497 X-HE-Meta: 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 ud6Rv4By xKd51nhXmat3Cj4aEpDaxhfreTeCZhm/WxxC/K/tR/HJZg7WG22qUGyVf6s0TmSgre0sV8I9Q5sDh+R/3+ZJmjfVgt1Gb9vMtqHBQX2JKBzMJw8e7ffgTc9y4RwobRD9JDSEvQdfIF+8VxEqfnncemkWBrpIBH4m9qVqMSsSGWpFnbvhvtVnGZbJkE3FHIvc0/lHMomqh1saE0ddjcwqwlPEHeER141CY0yaTei4t7TS/ptcs39e3zji/+7oYDzznudfFZ7yiKx+MfS1Z+a85aBjfdEOULfWyYldplrCaHwc4zB9UnlisGgutjGRiwr4ZjoS1/oP9/QM+NPlRdM+Ssm48YL8ShJ+fA/Rxt/mx1hLF8bkmEpKb647Tes9ybYB934nw1Efo2RFA6+hXXhhP8BrzLgfPkbuIdRYkKWBtGlIO71CPbm46Tu74qLgkaUfoVc1Tj/T2cFldq0oVADGIrWrHieTHlmbZhTxr 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 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? -- Michal Hocko SUSE Labs