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Wed, 28 May 2025 02:18:54 -0700 (PDT) Date: Wed, 28 May 2025 02:18:52 -0700 From: Breno Leitao To: Shakeel Butt Cc: Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , Andrew Morton , Chen Ridong , Greg Kroah-Hartman , Michal Hocko , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, Michael van der Westhuizen , Usama Arif , Pavel Begunkov , Rik van Riel Subject: Re: [PATCH] memcg: Always call cond_resched() after fn() Message-ID: References: <20250523-memcg_fix-v1-1-ad3eafb60477@debian.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: BE14220008 X-Stat-Signature: i456m6xn5abecnmu387y84gp5ebqsxi9 X-Rspam-User: X-HE-Tag: 1748423936-570545 X-HE-Meta: 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 Ycko+Hk5 hb5zmj8QfWz6SY0htmLpKKLhSTkTnZlYIl5kGhYgRWV7SNZMI1ETmvou0dhl6QGzinEw7CxWbNb7lZIbZbG9MogsvLX/77fVt5WkfSXSJOkVAum5MfAFTotKegNEpvd0KUTo8fBgT2vrTXgI2XC0gu1BcK/ry9nNPxZpoI46+jalqtyk5rXFqmOpmAXe6E4IFnMr/sbcsY4A2cElE74BDf1PwKdBL5eFXqQK340mfUZwBgYkMCZR0hQBcgKG86mBeRR0NXCYCLs1d5jBRWLqo0FiI5/T63/roIfiyq8zARh1yjEVZsrNNh7eew/qC3tJAO4iGyEkCYBP2enWm0xTDZIuRK/t/8kslYzB8kU2Rwa9y2dJvl09+mvGQG0pZRFoZ62pBDrrw5OpE8IQMiX0yTmH9Q1OHbx76wQ1WSmaSxB0qfTqoW1ocu1bhyxyx6s+tyzPE 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: Hello Shakeel, On Tue, May 27, 2025 at 09:54:10AM -0700, Shakeel Butt wrote: > On Tue, May 27, 2025 at 03:03:34AM -0700, Breno Leitao wrote: > > > > Not sure I followed you here. __oom_kill_process is doing the following: > > > > static void __oom_kill_process(struct task_struct *victim, const char *message) > > { > > ... > > pr_err("%s: Killed process %d (%s) total-vm:%lukB, anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB, UID:%u pgtables:%lukB oom_score_adj:%hd\n", > > > > > > Would you use a buffer to print to, and them flush it at the same time > > (with pr_err()?) > > > > Something similar to what mem_cgroup_print_oom_meminfo() does with > seq_buf. Right, where do you want to flush this buffer? I suppose we want to do it at once, in the caller (mem_cgroup_scan_tasks()), otherwise we will have the same problem, I would say. This is the code flow we are executing when I got this issue: mem_cgroup_scan_tasks() { for_each_mem_cgroup_tree(iter, memcg) { ret = fn(task, arg); //where fn() is oom_kill_memcg_member() oom_kill_memcg_member() { __oom_kill_process() { pr_info() pr_err() } } } } So, basically it prints one/two message(s) for each process, and goes to 2k processes, so, __oom_kill_process() is called 2k times when the memcg is dying out. mem_cgroup_print_oom_meminfo() seems a bit different, where it coalesces a bunch of message in the same function and print them all at the same time. Another option is to create a buffer to mem_cgroup_scan_tasks(), but then we need to pass it to all fn(), and pushing down the replacement of printk() by seq_buf_printf(). Is this what you meant? If so, another concern I have is the buffer size to be printed at once. Let's suppose we have 2k "Killed process..." message in the buffer. Do we want to print it at once? (without a cond_resched()?) Thanks for the discussion, --breno