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Tue, 24 Dec 2024 15:06:53 -0800 (PST) Received: from [2620:0:1008:15:cdf5:75d7:1c62:d741] ([2620:0:1008:15:cdf5:75d7:1c62:d741]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-219dc964e60sm95109615ad.16.2024.12.24.15.06.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 24 Dec 2024 15:06:52 -0800 (PST) Date: Tue, 24 Dec 2024 15:06:51 -0800 (PST) From: David Rientjes To: Chen Ridong cc: akpm@linux-foundation.org, 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, 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 v3] memcg: fix soft lockup in the OOM process In-Reply-To: <20241224025238.3768787-1-chenridong@huaweicloud.com> Message-ID: <8cf29751-7c71-52ff-5492-0019ca7b0e02@google.com> References: <20241224025238.3768787-1-chenridong@huaweicloud.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII On Tue, 24 Dec 2024, 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. > > watchdog: BUG: soft lockup - CPU#2 stuck for 23s! [VM Thread:1503066] > CPU: 2 PID: 1503066 Comm: VM Thread Kdump: loaded Tainted: G > Hardware name: Huawei Cloud OpenStack Nova, BIOS > RIP: 0010:console_unlock+0x343/0x540 > RSP: 0000:ffffb751447db9a0 EFLAGS: 00000247 ORIG_RAX: ffffffffffffff13 > RAX: 0000000000000001 RBX: 0000000000000000 RCX: 00000000ffffffff > RDX: 0000000000000000 RSI: 0000000000000004 RDI: 0000000000000247 > RBP: ffffffffafc71f90 R08: 0000000000000000 R09: 0000000000000040 > R10: 0000000000000080 R11: 0000000000000000 R12: ffffffffafc74bd0 > R13: ffffffffaf60a220 R14: 0000000000000247 R15: 0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 00007f2fe6ad91f0 CR3: 00000004b2076003 CR4: 0000000000360ee0 > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > Call Trace: > vprintk_emit+0x193/0x280 > printk+0x52/0x6e > dump_task+0x114/0x130 > mem_cgroup_scan_tasks+0x76/0x100 > dump_header+0x1fe/0x210 > oom_kill_process+0xd1/0x100 > out_of_memory+0x125/0x570 > mem_cgroup_out_of_memory+0xb5/0xd0 > try_charge+0x720/0x770 > mem_cgroup_try_charge+0x86/0x180 > mem_cgroup_try_charge_delay+0x1c/0x40 > do_anonymous_page+0xb5/0x390 > handle_mm_fault+0xc4/0x1f0 > > 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. > > Fixes: 9cbb78bb3143 ("mm, memcg: introduce own oom handler to iterate only over its own threads") > Signed-off-by: Chen Ridong Looks fine to me, although we do a lot of processes traversals for oom kill selection as well and this hasn't ever popped up as a significant concern. We have cases far beyond 56k processes. No objection to the approach, however.