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Tue, 14 Jan 2025 09:20:29 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id 0XoCFV0shmdWdQAAD6G6ig (envelope-from ); Tue, 14 Jan 2025 09:20:29 +0000 Message-ID: Date: Tue, 14 Jan 2025 10:20:28 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] memcg: fix soft lockup in the OOM process Content-Language: en-US To: Michal Hocko , Andrew Morton Cc: Chen Ridong , hannes@cmpxchg.org, yosryahmed@google.com, roman.gushchin@linux.dev, shakeel.butt@linux.dev, muchun.song@linux.dev, davidf@vimeo.com, handai.szj@taobao.com, rientjes@google.com, kamezawa.hiroyu@jp.fujitsu.com, RCU , linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, chenridong@huawei.com, wangweiyang2@huawei.com References: <20241224025238.3768787-1-chenridong@huaweicloud.com> <1ea309c1-d0f8-4209-b0b0-e69ad4e986ae@suse.cz> <58caaa4f-cf78-4d0f-af31-8a9277b6ebf5@huaweicloud.com> <20250113194546.3de1af46fa7a668111909b63@linux-foundation.org> From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Spam-Level: X-Spamd-Result: default: False [-4.30 / 50.00]; BAYES_HAM(-3.00)[99.99%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MID_RHS_MATCH_FROM(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; MIME_TRACE(0.00)[0:+]; ARC_NA(0.00)[]; RCPT_COUNT_TWELVE(0.00)[18]; RCVD_TLS_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; FUZZY_BLOCKED(0.00)[rspamd.com]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo,suse.cz:mid] X-Spam-Score: -4.30 X-Spam-Flag: NO On 1/14/25 09:40, Michal Hocko wrote: > On Mon 13-01-25 19:45:46, Andrew Morton wrote: >> On Mon, 13 Jan 2025 14:51:55 +0800 Chen Ridong wrote: >> >> > >> @@ -430,10 +431,15 @@ static void dump_tasks(struct oom_control *oc) >> > >> mem_cgroup_scan_tasks(oc->memcg, dump_task, oc); >> > >> else { >> > >> struct task_struct *p; >> > >> + int i = 0; >> > >> >> > >> rcu_read_lock(); >> > >> - for_each_process(p) >> > >> + for_each_process(p) { >> > >> + /* Avoid potential softlockup warning */ >> > >> + if ((++i & 1023) == 0) >> > >> + touch_softlockup_watchdog(); >> > > >> > > This might suppress the soft lockup, but won't a rcu stall still be detected? >> > >> > Yes, rcu stall was still detected. "was" or "would be"? I thought only the memcg case was observed, or was that some deliberate stress test of the global case? (or the pr_info() console stress test mentioned earlier, but created outside of the oom code?) >> > For global OOM, system is likely to struggle, do we have to do some >> > works to suppress RCU detete? >> >> rcu_cpu_stall_reset()? > > Do we really care about those? The code to iterate over all processes > under RCU is there (basically) since ever and yet we do not seem to have > many reports of stalls? Chen's situation is specific to memcg OOM and > touching the global case was mostly for consistency reasons. Then I'd rather not touch the global case then if it's theoretical? It's not even exactly consistent, given it's a cond_resched() in the memcg code (that can be eventually automatically removed once/if lazy preempt becomes the sole implementation), but the touch_softlockup_watchdog() would remain, while doing only half of the job?