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([2601:188:c102:b180:1f8b:71d0:77b1:1f6e]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-4edb56e2173sm55990661cf.2.2025.11.11.12.44.07 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 11 Nov 2025 12:44:08 -0800 (PST) From: Waiman Long X-Google-Original-From: Waiman Long Message-ID: <061cdd9e-a70b-4d45-909a-6d50f4da8ef3@redhat.com> Date: Tue, 11 Nov 2025 15:44:07 -0500 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH mm-new v3] mm/memcontrol: Add memory.stat_refresh for on-demand stats flushing To: Michal Hocko , 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 References: <20251110101948.19277-1-leon.huangfu@shopee.com> <9a9a2ede-af6e-413a-97a0-800993072b22@redhat.com> In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: PzuGnHveMzFt5BjrU2Sr-DTsKZQ-SdcexJNuzxasy8k_1762893850 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 293134000E X-Stat-Signature: u7wnp8e8jycmwtgzonyjswmn4zbocsex X-HE-Tag: 1762893852-695466 X-HE-Meta: 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 mT+TsAfY 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 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 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. Cheers, Longman