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Thu, 04 Dec 2025 10:28:55 -0800 (PST) Received: from localhost ([2603:7000:c01:2716:929a:4aff:fe16:c778]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-88827f49e51sm15291736d6.15.2025.12.04.10.28.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 04 Dec 2025 10:28:54 -0800 (PST) Date: Thu, 4 Dec 2025 13:28:50 -0500 From: Johannes Weiner To: Chen Ridong Cc: akpm@linux-foundation.org, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, david@kernel.org, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, corbet@lwn.net, roman.gushchin@linux.dev, shakeel.butt@linux.dev, muchun.song@linux.dev, yuzhao@google.com, zhengqi.arch@bytedance.com, linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, lujialin4@huawei.com, chenridong@huawei.com Subject: Re: [RFC PATCH -next 1/2] mm/mglru: use mem_cgroup_iter for global reclaim Message-ID: <20251204182850.GA481418@cmpxchg.org> References: <20251204123124.1822965-1-chenridong@huaweicloud.com> <20251204123124.1822965-2-chenridong@huaweicloud.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251204123124.1822965-2-chenridong@huaweicloud.com> X-Rspamd-Queue-Id: 9A3B220006 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: 4m9m6c3gdgpi6jc7ncmgpdjih3e88p1y X-HE-Tag: 1764872936-745768 X-HE-Meta: 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 UPti3Be3 vaWBcdTRcclUChAyP+TEI31SgJNKgC0tQKha+HOczYUZvchmbFUFfabYFgOY7ajoIJLp1fSUmoAkZDW7iW2dw1F/5n8XQ74mU8kV247UEEboR48ZW5ysG50Wu7etidHPS/TQ0eomP7tv5yyG8TPMXjxf4rPtqmlNtVXvzMi451B74zx+CrC4wsJKxEOBkLmceJYcVu2NcAG2+3mer4sRapWnqcOlaAK/M3qrE4pdLLTvs+v7SjBS493pEk4PophVikSnY7egXvWE772XqoRZEVfLDrbYX1giHT/pwAheo59URE0vjDDVdUlfhKasv/y1lfQAnqoLNvG6JY3vjYojcC89UyBEk32W1iPAJ+PlusfHAV90we2NZGmkCIAx6PMS5Il31xpSu7xrTvCiCGsLw8E78n5+y5jxz0wPoHh5ZGBT/AToSDGhCEkUrAhWOg1NVMI9qdUlzdig4EiSWsLb6wf2ZhSki4d1iubuyBno1jqiyc7pAGr4olPs5VYxwzWww0srXtIfbluG6agbpZ9EvJwKKDmGrX5DFIUg/SYrUJTnM8+QvMh8uKwB8b/+ZQ9+EnjEsVMTl47nLQlvezDxc6Gc7siifWq5L6gfv 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 Thu, Dec 04, 2025 at 12:31:23PM +0000, Chen Ridong wrote: > From: Chen Ridong > > The memcg LRU was originally introduced for global reclaim to enhance > scalability. However, its implementation complexity has led to performance > regressions when dealing with a large number of memory cgroups [1]. > > As suggested by Johannes [1], this patch adopts mem_cgroup_iter with > cookie-based iteration for global reclaim, aligning with the approach > already used in shrink_node_memcgs. This simplification removes the > dedicated memcg LRU tracking while maintaining the core functionality. > > It performed a stress test based on Zhao Yu's methodology [2] on a > 1 TB, 4-node NUMA system. The results are summarized below: > > memcg LRU memcg iter > stddev(pgsteal) / mean(pgsteal) 91.2% 75.7% > sum(pgsteal) / sum(requested) 216.4% 230.5% > > The new implementation demonstrates a significant improvement in > fairness, reducing the standard deviation relative to the mean by > 15.5 percentage points. While the reclaim accuracy shows a slight > increase in overscan (from 85086871 to 90633890, 6.5%). > > The primary benefits of this change are: > 1. Simplified codebase by removing custom memcg LRU infrastructure > 2. Improved fairness in memory reclaim across multiple cgroups > 3. Better performance when creating many memory cgroups > > [1] https://lore.kernel.org/r/20251126171513.GC135004@cmpxchg.org > [2] https://lore.kernel.org/r/20221222041905.2431096-7-yuzhao@google.com > Signed-off-by: Chen Ridong Acked-by: Johannes Weiner The diff and the test results look good to me. Comparing the resulting shrink_many() with shrink_node_memcgs(), this also looks like a great step towards maintainability and unification. Thanks!