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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 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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> Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit 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