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Mon, 02 Nov 2026 03:40:36 -0800 (PST) Received: from osman.mioffice.cn ([43.224.245.178]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2eb39262c47sm26652745ad.38.2026.11.02.03.40.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 02 Nov 2026 03:40:35 -0800 (PST) From: Zhan Xusheng To: mhocko@suse.com Cc: akpm@linux-foundation.org, hannes@cmpxchg.org, roman.gushchin@linux.dev, shakeel.butt@linux.dev, muchun.song@linux.dev, penguin-kernel@i-love.sakura.ne.jp, tj@kernel.org, mkoutny@suse.com, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, zhanxusheng@xiaomi.com Subject: Re: [PATCH] mm: memcontrol: don't miss processes whose leader has exited in OOM scans Date: Mon, 2 Nov 2026 19:40:29 +0800 Message-ID: <20261102114029.1259655-1-zhanxusheng1024@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: References: X-Archived-By: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 5D8FB100006 X-Stat-Signature: mcc9e1fzcaj8f5eragbq566gje37ru7y X-Spam-Status: No, score=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_GIT autolearn=no autolearn_force=no version=4.0.1 X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1793619637-630085 X-HE-Meta: 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 BYD0ZH2+ hX/pHCyAXeG/0BeUgLizS++xK2jTpnElXrkgNxQvvMg8EKZHjpqy/cNCBYDmSaS6y+sMtgulNCLcD4vLQHzJMQDRJNcQ1tZTeyI8oHS1URl3ssKyOXcoXsGqomK2/VtZXNiiuimldLxHdz/ujSDsx112T0P4HBpfADoMgz8C/PN0g3Qc37KgFmr/uwHAwOnNvznVaILs9WbsBK0WdxMIyNWbeAj5qXUuqBJiDXxiQCCH+i/F5hxRukvXKVBEk0b4Ihai1hYaAgMgA3csDHfPGhiP5eaLpdxmf+BTr6KWnFiPLybB29RL2GIV9yxTPi9wV4/QpwU4iwFL78oH1f7cOz9TIfGvKCFXAyVUvrThemcAQdPOVBT/VqdL0DtO0Xj+80gUJ1lBqCZQZ9QNipFyLBjNdsJOHNpgMZbTi9S05ZxjeTVxMx/EYMmbYvg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 Hi Michal, This is v1. v2 [1] reworked the check, but your questions apply to both. On Mon, Nov 02, 2026 at 11:12:42AM +0100, Michal Hocko wrote: > Is this a desirable/intended behavior? Shouldn't we move the dead leader > along with the rest? Userspace sees it too. After writing the PID of such a process to dst/cgroup.procs: src: cgroup.procs = 85 cgroup.threads = (empty) dst: cgroup.procs = (empty) cgroup.threads = 86 87 Moving the leader would fix that, and memcg would then need no change, as the PROCS walk already returns a dying leader with live threads. The catch is that the leader has already gone through cgroup_task_dead() and is still accounted by controllers: pids, for one, uncharges it through task_css() when it is reaped, so the move would also have to transfer its pids charge. Tejun, would that be acceptable in the core? > Should CSS_TASK_ITER_PROCS iteration see all processes > regardless leader being alive after or prior the migration? With the leader moved, it would. Otherwise PROCS would have to pick a stand-in thread, which is what this patch does inside memcg. > Shouldn't this be CSS_TASK_ITER_THREADED instead of 0? No. Walking a memcg css goes over e_csets[memory], which already includes the csets of threaded descendants, as memory is not a threaded controller. THREADED also walks each cset's threaded_csets, so those would be visited twice. It is meant for walks over cgrp->self, like cgroup.procs. 0 is also what this function used before f168a9a54ec3. [1] https://lore.kernel.org/all/20261027144016.2582880-1-zhanxusheng1024@gmail.com/ Thanks, Zhan Xusheng