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b=EKV4BkfZxIDTwzIEz9hKHZp/wbKXwx29zPj9wQSpSdtpkCeJlKF/D4Y0vDeEBRfG0 /EAd4l4sZ+mtmtVq3GIu4ohjlURL74OkjwxG/eEdSksBEgzqhfT1LQoglCuKEUBqzv jeLYNZnnlX+3o5HjCh4+LH6mhZ9/YKWmp9w7+lRY= Date: Fri, 20 Dec 2024 14:47:34 -0800 From: Andrew Morton To: Chen Ridong Cc: mhocko@kernel.org, hannes@cmpxchg.org, yosryahmed@google.com, roman.gushchin@linux.dev, shakeel.butt@linux.dev, muchun.song@linux.dev, davidf@vimeo.com, vbabka@suse.cz, handai.szj@taobao.com, rientjes@google.com, kamezawa.hiroyu@jp.fujitsu.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, chenridong@huawei.com, wangweiyang2@huawei.com Subject: Re: [PATCH v2] memcg: fix soft lockup in the OOM process Message-Id: <20241220144734.05d62ef983fa92e96e29470d@linux-foundation.org> In-Reply-To: <20241220103123.3677988-1-chenridong@huaweicloud.com> References: <20241220103123.3677988-1-chenridong@huaweicloud.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: E5037C001C X-Stat-Signature: wj5p8hoe796kcesskdhaspfrzo6gxdbn X-Rspam-User: X-HE-Tag: 1734734818-386468 X-HE-Meta: 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 J95FeAc6 yhCLYATugSDVKEbfUgmKIlXUeqGr7RFKsAGdppz33AMeNsRFzdjKkt7U99Aj7x0yyQFC9Ok5+fot06zRum4BMwrYBZSLb4jvLLY/2OXUmmc7OxFORts+5Z6YV1QB7HRmkoMCgFfON8a8jF4/ZIWWUs7M3DAPu5j0dxtlmpX9CSdRJHmEAN1WAke4ynw6VKHPvOJ/gzvLbw+4viiud679V7a22otPFcR9tdJfn37YupgoCKbptglovqw/nwEkhZc8rbu3BRlTPRpWfcI7FgxiPqv/RrB+s9zjAoRWN5IaT/hE+5UY= 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, 20 Dec 2024 10:31:23 +0000 Chen Ridong wrote: > From: Chen Ridong > > A soft lockup issue was found in the product with about 56,000 tasks were > in the OOM cgroup, it was traversing them when the soft lockup was > triggered. > > ... > > This is because thousands of processes are in the OOM cgroup, it takes a > long time to traverse all of them. As a result, this lead to soft lockup > in the OOM process. > > To fix this issue, call 'cond_resched' in the 'mem_cgroup_scan_tasks' > function per 1000 iterations. For global OOM, call > 'touch_softlockup_watchdog' per 1000 iterations to avoid this issue. > > ... > > --- a/include/linux/oom.h > +++ b/include/linux/oom.h > @@ -14,6 +14,13 @@ struct notifier_block; > struct mem_cgroup; > struct task_struct; > > +/* When it traverses for long time, to prevent softlockup, call > + * cond_resched/touch_softlockup_watchdog very 1000 iterations. > + * The 1000 value is not exactly right, it's used to mitigate the overhead > + * of cond_resched/touch_softlockup_watchdog. > + */ > +#define SOFTLOCKUP_PREVENTION_LIMIT 1000 If this is to have potentially kernel-wide scope, its name should identify which subsystem it belongs to. Maybe OOM_KILL_RESCHED or something. But I'm not sure that this really needs to exist. Are the two usage sites particularly related? > enum oom_constraint { > CONSTRAINT_NONE, > CONSTRAINT_CPUSET, > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 5c373d275e7a..f4c12d6e7b37 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -1161,6 +1161,7 @@ void mem_cgroup_scan_tasks(struct mem_cgroup *memcg, > { > struct mem_cgroup *iter; > int ret = 0; > + int i = 0; > > BUG_ON(mem_cgroup_is_root(memcg)); > > @@ -1169,8 +1170,11 @@ void mem_cgroup_scan_tasks(struct mem_cgroup *memcg, > struct task_struct *task; > > css_task_iter_start(&iter->css, CSS_TASK_ITER_PROCS, &it); > - while (!ret && (task = css_task_iter_next(&it))) > + while (!ret && (task = css_task_iter_next(&it))) { > ret = fn(task, arg); > + if (++i % SOFTLOCKUP_PREVENTION_LIMIT) And a modulus operation is somewhat expensive. Perhaps a simple /* Avoid potential softlockup warning */ if ((++i & 1023) == 0) at both sites will suffice. Opinions might vary...