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h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=KFLIycYleDqFqiPTvzcuWrEnQKh2Pb50OV9U0Zi5AXqeSMrmz6u2vtVmM/SzZQGvx Tharxb/y5DzlXbkOUihqC6pTa9UnX5G1Zwzynh785MP0voCVZJnOQqNvpoqxurdQw5 JgKXSHrlSuKE37knqmDuZlQnZwmJvCAbQd6i2ACIFt0FRvTHP9K0S4hdWL7+ZJKEvq kYHqa963FYR1h5Rb3E5NSf9zAKKbiAe5i8dRh3+NkT3k+Y1EBFRirXLClB+WOJZ9Vf idkCZnBb+c87k1LoZVVVntapTvP4wJqZctSNwno24WoR5KTWMw/pMfRpuWgoHGkw4l LnO0OkRJR4J1g== Received: by mail-ed1-f48.google.com with SMTP id 4fb4d7f45d1cf-65f980cea07so3437634a12.0 for ; Fri, 27 Feb 2026 10:18:33 -0800 (PST) X-Forwarded-Encrypted: i=1; AJvYcCUYandsfL7OEeFn7k5BtXIx96q7YPFOo2rvxwLu7VG/KkpQEPaMnO2UKb1e/IOot06a/ZSDgwSs8Q==@kvack.org X-Gm-Message-State: AOJu0YyKdn2wF8Tt1St8HDizMoi6ZgPZh6MtcHw3izH1obr2t4XErhq+ G28bCRYfa+TvGZmWzcrsNOmH+q/U0Jzus2zxFV51uQ207dqcp51ddMKSxN+ZqoijC/Nnt8bdIPL LDMCOp0g8By2q5pgoXW9glmVJcuuAqRI= X-Received: by 2002:a17:907:847:b0:b70:b700:df98 with SMTP id a640c23a62f3a-b937636ceaemr277939266b.5.1772216312497; Fri, 27 Feb 2026 10:18:32 -0800 (PST) MIME-Version: 1.0 References: <97e296ed-ef73-44b7-ab68-3d79749caa47@linux.dev> In-Reply-To: From: Yosry Ahmed Date: Fri, 27 Feb 2026 10:18:21 -0800 X-Gmail-Original-Message-ID: X-Gm-Features: AaiRm50TLXHVX5j7xS88WvrO4MStBAuGwnOEEW7p2oMKLrYDnofUaDeqDh7Zhl0 Message-ID: Subject: Re: [PATCH v5 29/32] mm: memcontrol: prepare for reparenting non-hierarchical stats To: Qi Zheng Cc: Shakeel Butt , hannes@cmpxchg.org, hughd@google.com, mhocko@suse.com, roman.gushchin@linux.dev, muchun.song@linux.dev, david@kernel.org, lorenzo.stoakes@oracle.com, ziy@nvidia.com, harry.yoo@oracle.com, yosry.ahmed@linux.dev, imran.f.khan@oracle.com, kamalesh.babulal@oracle.com, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, chenridong@huaweicloud.com, mkoutny@suse.com, akpm@linux-foundation.org, hamzamahfooz@linux.microsoft.com, apais@linux.microsoft.com, lance.yang@linux.dev, bhe@redhat.com, usamaarif642@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Qi Zheng Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: B8606180004 X-Stat-Signature: wqhuw71fhrnkhmudghmx3icgpc7pcb9x X-Rspam-User: X-HE-Tag: 1772216314-332649 X-HE-Meta: U2FsdGVkX1+h3UFFYhv7gllVz1+rH97bApEY8opMSjzahUDEFBHUwepykTFHWsUv2eLmAByiUgoPBBFceaXbnp7zMsE1A9ii9UVVk1xh4nTwTnely3sKLCSTozN+FM90SYlYgyDBPLXmBctaMsftPeJRfR5i48HyZNnnYsFQVhzMPHDOquwOLpjAKGGRTmwyvO3lE9lkTvYe48B6bqjL4so7od7Xe93qYSh4TxXj7vVT+qlkls1CpKnJDe65E8WoOYbCpexXi8H4fNnJ3ATI1G708f0NMU/mqTEFE9KZpdssmQWTTsM/73DawyrQMJB0n9wsmnT5bi3MfrWiB5lD+NH8lxWIuZTQBmM84H7BC30KbMgxYwdBjNcmqWAz0rxqvPs48VV947DJZvBlg2xDmkhvcJu4V5viN/6F6RwIie5FCpBsClogW1hDuwGzqZrFCb0ihoUKVV0hG4gbnh3fcK9UoXfEDXYyNvU9gATgZJqjGN88nyQDgv4QCy/AxJb1H4UNYo/eeLOBPgZ1YHleKGw6qcklDH9fUxx4qoIw2TRS1UxmFEwEiPc5QG5hoExob3s4YWKsyjFffn1k1Rs64WDLmmKxtPWyzokFyZUxRpjaQncHMbbXDWtsOgHTirgrgNuZXvQnwLX921PqOvfp/FwWkehtAd9LKNhL7RAZ+qoqNP11h88/SgjebAga9nI7V4seCHSwBVq/qJVH+zOqhZcOw1zMhFgsMrwAeW3g1CkNTh7P6lg4kd4cXRpT2Khx/6UTCin+HHbEliVPsubuIOxqip91G/uVVNBAGkwqzBknDnWCmkgR4jvzUiwTpafABYqQ9n+MPgm6raYituswAoRGEmY9p1W80kz2mUjQAWWWJXvdl55kI/7thmTwiO3QoKeO1WIYePmD0ZQWz3bndIE0njIcAxROyeMn6DxCHgAt9kDgu3quAQTozcsFxc+li17rD6eZUAZQErIUiwG QJ/s+UjE XqyoCK0IA1VVigiufXU/IvG8/D2Uq9BR7ul8B2nQzBuV3yU5CFUZeeRSSe7ApCxcU/590wotXNj5qExNYXLSc2xTYpCaxjtxEkzNDKK6gp6A/IT6k2MPbC7tdYowrk6y5w0P9Ueuoof/DcKtPZwGKOahdUvO7MoazKUMgCdSGRR0kT73qXJ+PO4E3ETC6P1WEijrHtSjRbO+FrULGhtFWMaS1y+FR3yIF+Tr3VONNHORJI27vBdvpdXJ8LEk22jb3QZlUB9Es0rdHy8YEmEOJYL4oiUxlRwXAx/Eo Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: [..] > >> @@ -506,12 +517,10 @@ void reparent_memcg_lruvec_state_local(struct > >> mem_cgroup *memcg, > >> for_each_node(nid) { > >> struct lruvec *child_lruvec = mem_cgroup_lruvec(memcg, > >> NODE_DATA(nid)); > >> struct lruvec *parent_lruvec = > >> mem_cgroup_lruvec(parent, NODE_DATA(nid)); > >> - struct mem_cgroup_per_node *parent_pn; > >> unsigned long value = > >> lruvec_page_state_local(child_lruvec, idx); > >> > >> - parent_pn = container_of(parent_lruvec, struct > >> mem_cgroup_per_node, lruvec); > >> - > >> - atomic_long_add(value, > >> &(parent_pn->lruvec_stats->state_local[i])); > >> + mod_memcg_lruvec_state(child_lruvec, idx, -value); > > > > We can't use mod_memcg_lruvec_state() here, because child memcg has > > already been set CSS_DYING. So in mod_memcg_lruvec_state(), we will > > get parent memcg. > > > > It seems we need to reimplement a function or add a parameter to > > mod_memcg_lruvec_state() to solve the problem. What do you think? > > Since child memcg is about to disappear, perhaps we can just add value > to parent memcg without handling the child memcg. Make sense? Ugh yes, I missed that, thanks. I don't think we can just leave the child's memcg wrong. Aside from the fact that I would be nervous if access to those stats is still possible after it's offlined (e.g. can userspace already have the stats file open, or maybe some in-kernel code uses it), there's a bigger issue. When the child cgroup is released, css_release_work_fn() will flush its stats and then it will be double counted at the parent. Maybe refactor the part sof mod_memcg_lruvec_state() and mod_memcg_state () without get_non_dying_memcg_{start/end}() into helpers, and call that directly from the reparenting functions? Adding a boolean argument to mod_memcg_lruvec_state() and mod_memcg_state() will add a lot of churn, and naked boolean arguments are not ideal.