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Mon, 10 Nov 2025 22:12:22 -0800 (PST) From: Leon Huang Fu To: mhocko@suse.com Cc: akpm@linux-foundation.org, cgroups@vger.kernel.org, corbet@lwn.net, hannes@cmpxchg.org, jack@suse.cz, joel.granados@kernel.org, kyle.meyer@hpe.com, lance.yang@linux.dev, laoar.shao@gmail.com, leon.huangfu@shopee.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, mclapinski@google.com, mkoutny@suse.com, muchun.song@linux.dev, roman.gushchin@linux.dev, shakeel.butt@linux.dev, tj@kernel.org Subject: Re: [PATCH mm-new v3] mm/memcontrol: Add memory.stat_refresh for on-demand stats flushing Date: Tue, 11 Nov 2025 14:12:13 +0800 Message-ID: <20251111061214.70785-1-leon.huangfu@shopee.com> X-Mailer: git-send-email 2.51.2 In-Reply-To: References: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: DDB4614000E X-Stat-Signature: c3fpq46io7uz1ab13u5xoqjybjp8rftg X-Rspamd-Server: rspam02 X-Rspam-User: X-HE-Tag: 1762841543-319624 X-HE-Meta: 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 AkgJCHGc 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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 Mon, Nov 10, 2025 at 7:28 PM Michal Hocko wrote: > > On Mon 10-11-25 18:19:48, Leon Huang Fu wrote: > > Memory cgroup statistics are updated asynchronously with periodic > > flushing to reduce overhead. The current implementation uses a flush > > threshold calculated as MEMCG_CHARGE_BATCH * num_online_cpus() for > > determining when to aggregate per-CPU memory cgroup statistics. On > > systems with high core counts, this threshold can become very large > > (e.g., 64 * 256 = 16,384 on a 256-core system), leading to stale > > statistics when userspace reads memory.stat files. > > > > This is particularly problematic for monitoring and management tools > > that rely on reasonably fresh statistics, as they may observe data > > that is thousands of updates out of date. > > > > Introduce a new write-only file, memory.stat_refresh, that allows > > userspace to explicitly trigger an immediate flush of memory statistics. > > Writing any value to this file forces a synchronous flush via > > __mem_cgroup_flush_stats(memcg, true) for the cgroup and all its > > descendants, ensuring that subsequent reads of memory.stat and > > memory.numa_stat reflect current data. > > > > This approach follows the pattern established by /proc/sys/vm/stat_refresh > > and memory.peak, where the written value is ignored, keeping the > > interface simple and consistent with existing kernel APIs. > > > > Usage example: > >   echo 1 > /sys/fs/cgroup/mygroup/memory.stat_refresh > >   cat /sys/fs/cgroup/mygroup/memory.stat > > > > The feature is available in both cgroup v1 and v2 for consistency. > > > > Signed-off-by: Leon Huang Fu > > Acked-by: Michal Hocko > Thanks! > Thank you for your review. Thanks, Leon [...]