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From: Shakeel Butt To: Andrew Morton Cc: Michal Hocko , David Rientjes , Johannes Weiner , Roman Gushchin , Muchun Song , Suren Baghdasaryan , Usama Arif , Rik van Riel , Nhat Pham , Meta kernel team , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] memcg: bypass the reclaim and oom killer for dying tasks once oom_reaper is done Message-ID: References: <20260729024612.3369005-1-shakeel.butt@linux.dev> <20260729181349.fd41f1a09ec19c9cfb0c412f@linux-foundation.org> 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 Content-Disposition: inline In-Reply-To: <20260729181349.fd41f1a09ec19c9cfb0c412f@linux-foundation.org> X-Migadu-Flow: FLOW_OUT On Wed, Jul 29, 2026 at 06:13:49PM -0700, Andrew Morton wrote: > On Tue, 28 Jul 2026 19:46:12 -0700 Shakeel Butt wrote: > > > At Meta, we are seeing instances where an OOM killed job is stuck in the > > exit path for several hours. In one particular case, the job was stuck > > for more than 8 hours and I had to manually remove the memory.max limits > > to allow the process to exit. > > Not seeing the problem here - that sounds like normal kernel behavior ;) > > > Reproduced with 20k threads, each parking a robust futex head on > > its own zswapped page, OOM-group-killed while a sibling holds mmap_lock > > for write so the reaper gives up and sets MMF_OOM_SKIP. Tested on > > next-20260728 and baseline show ~90 seconds exit time while with the > > patch the exit time reduced to ~3 seconds. > > Very positive. > > But it doesn't sound like you're fully confident that the problem is > fully solved? Yes as I am not able to reproduce multi hour stall, so I might be missing something else. The patch at least fixes the issue which I am able to reproduce. > > > --- a/mm/memcontrol.c > > +++ b/mm/memcontrol.c > > @@ -2653,6 +2653,19 @@ static int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask, > > if (!gfpflags_allow_blocking(gfp_mask)) > > goto nomem; > > > > + /* > > + * OOM victim still needs to charge memory to exit. OOM reaper should > > + * help but it might fail on mmap_lock contention. If the victim is a > > + * large thread group then all exiting threads might compete on oom_lock > > + * just to learn that there is nothing really killable anymore. Bail > > + * out early and fail the charge to expedite their exit. They are > > + * considered fully reclaimed by the oom reaper and they shouldn't > > + * contribute further charges. > > + */ > > + if (tsk_is_oom_victim(current) && > > + mm_flags_test(MMF_OOM_SKIP, current->signal->oom_mm)) > > + goto nomem; > > + > > __memcg_memory_event(mem_over_limit, MEMCG_MAX, allow_spinning); > > raised_max_event = true; > > Should we backport this? I don't have any strong opinion. I wanted to deploy this patch in Meta fleet to get some exposure. Maybe backporting will give more exposure to it.