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Mon, 23 Feb 2026 08:36:59 -0800 (PST) Received: from localhost ([2603:7000:c00:3a00:365a:60ff:fe62:ff29]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-8997e7747f0sm72340136d6.51.2026.02.23.08.36.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 23 Feb 2026 08:36:58 -0800 (PST) Date: Mon, 23 Feb 2026 11:36:55 -0500 From: Johannes Weiner To: Kairui Song via B4 Relay Cc: linux-mm@kvack.org, Andrew Morton , David Hildenbrand , Lorenzo Stoakes , Zi Yan , Baolin Wang , Barry Song , Hugh Dickins , Chris Li , Kemeng Shi , Nhat Pham , Baoquan He , Yosry Ahmed , Youngjun Park , Chengming Zhou , Roman Gushchin , Shakeel Butt , Muchun Song , Qi Zheng , linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Kairui Song Subject: Re: [PATCH RFC 08/15] mm, swap: store and check memcg info in the swap table Message-ID: References: <20260220-swap-table-p4-v1-0-104795d19815@tencent.com> <20260220-swap-table-p4-v1-8-104795d19815@tencent.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260220-swap-table-p4-v1-8-104795d19815@tencent.com> X-Stat-Signature: zwgk78antgetiuw99symgt14qhpqj8ea X-Rspamd-Server: rspam11 X-Rspam-User: X-Rspamd-Queue-Id: E903D40003 X-HE-Tag: 1771864620-325484 X-HE-Meta: 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 qLTtHawN 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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 Fri, Feb 20, 2026 at 07:42:09AM +0800, Kairui Song via B4 Relay wrote: > From: Kairui Song > > To prepare for merging the swap_cgroup_ctrl into the swap table, store > the memcg info in the swap table on swapout. > > This is done by using the existing shadow format. > > Note this also changes the refault counting at the nearest online memcg > level: > > Unlike file folios, anon folios are mostly exclusive to one mem cgroup, > and each cgroup is likely to have different characteristics. This is not correct. As much as I like the idea of storing the swap_cgroup association inside the shadow entry, the refault evaluation needs to happen at the level that drove eviction. Consider a workload that is split into cgroups purely for accounting, not for setting different limits: workload (limit domain) `- component A `- component B This means the two components must compete freely, and it must behave as if there is only one LRU. When pages get reclaimed in a round-robin fashion, both A and B get aged at the same pace. Likewise, when pages in A refault, they must challenge the *combined* workingset of both A and B, not just the local pages. Otherwise, you risk retaining stale workingset in one subgroup while the other one is thrashing. This breaks userspace expectations.