From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id AB5E1C53219 for ; Tue, 28 Jul 2026 16:55:48 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 8F0A66B007B; Tue, 28 Jul 2026 12:55:47 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 8C7DF6B0088; Tue, 28 Jul 2026 12:55:47 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 7BACD6B0096; Tue, 28 Jul 2026 12:55:47 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id 4EF136B007B for ; Tue, 28 Jul 2026 12:55:47 -0400 (EDT) Received: from smtpin16.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay03.hostedemail.com (Postfix) with ESMTP id BFDF5A0406 for ; Tue, 28 Jul 2026 16:55:46 +0000 (UTC) X-FDA: 85038787092.16.259AA0C Received: from out-177.mta1.migadu.com (out-177.mta1.migadu.com [95.215.58.177]) by imf10.hostedemail.com (Postfix) with ESMTP id 3849EC000A for ; Tue, 28 Jul 2026 16:55:42 +0000 (UTC) Authentication-Results: imf10.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=nzriWRMo; spf=pass (imf10.hostedemail.com: domain of shakeel.butt@linux.dev designates 95.215.58.177 as permitted sender) smtp.mailfrom=shakeel.butt@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1785257745; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=r5JlP6ioUX+/TbxbJL0DU8jGeR7d++HxnQJa+9ff9G4=; b=ERINx1GOqYeNI9JQQ7uD2ZOIq2wsuc5OIjDW5VA271c9+jp38eD7J92v0dmCtyYO/5ShHj fPyCBrdIUYx3dcxArR0clAHH2GDLCB9w02xlqAKp+NtJJ/Sj1MWx3cC5LmK7Z4DJMbs1vu ZAS2323oXmPgnQHI8nLBoXuax5IrcrQ= ARC-Authentication-Results: i=1; imf10.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=nzriWRMo; spf=pass (imf10.hostedemail.com: domain of shakeel.butt@linux.dev designates 95.215.58.177 as permitted sender) smtp.mailfrom=shakeel.butt@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1785257745; b=AbWTe6JjEBm37HjVQcbziE8/Xia6XOMHJE+IYHITsGl3G1Iwtf5ZDlJJ17SmcGU1e75CKP eqR39MP9Ez/UVZDR7P4uiNSwd0ypQv3ZpYO3UqYjKHdjKy0HBIT3frzu1LQ13juPO3NOdC Um4SGHh/uzqEUTkGhtQFP61cm2oKHkU= Date: Tue, 28 Jul 2026 09:55:21 -0700 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1785257740; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=r5JlP6ioUX+/TbxbJL0DU8jGeR7d++HxnQJa+9ff9G4=; b=nzriWRMoPg/hlP/vXaFpykit9EB3DnLvs8Agjmn21AqnYWpvMInnIAWS8vM5GTeHOWuVBA GIjg2BePJN+1JkLrhCPwC3yKVQVWuo3/+KZhKYvXxcAsZnmqH6tLTUSwLSG+LlT3DPP9f5 EG9bfe3zO9W22+H2NrI3/c7wWCR0gro= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Shakeel Butt To: Michal Hocko Cc: Andrew Morton , David Rientjes , Johannes Weiner , Roman Gushchin , Muchun Song , Thomas Gleixner , Ingo Molnar , Suren Baghdasaryan , Usama Arif , Peter Zijlstra , Darren Hart , Davidlohr Bueso , =?utf-8?B?QW5kcsOp?= Almeida , "Liam R . Howlett" , Yosry Ahmed , Rik van Riel , Nhat Pham , Meta kernel team , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC] Robust futex causing memcg OOM storm on exit Message-ID: References: <20260723001908.4046643-1-shakeel.butt@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: 3849EC000A X-Rspam-User: X-Stat-Signature: a5akubkimn8pqqdkmcraitcqk4caurud X-Rspamd-Server: rspam04 X-HE-Tag: 1785257742-256273 X-HE-Meta: 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 BhlVBPsc nDOwk5lbBT2ZToBusNKVbzjFiFmvazHfVugSOy2l4V/Dux5GRRRDfUM830SdrttG5zyg+xMqqN6t/tp5+33ZP3DaysLA/PMjlQKvSRLtXceYuplvf3nbVOOR3jafEdGpu7NrAoKgkI0Hr6HthIH1wUVWY80NThsnWaDTi4HmcAF8N/C6sReSXHzuZzpWjsHcNNTTIIfzvSslsukS7d9deaNgXtg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Jul 28, 2026 at 09:27:39AM +0200, Michal Hocko wrote: > On Mon 27-07-26 13:48:58, Shakeel Butt wrote: > > On Mon, Jul 27, 2026 at 08:38:37AM -0700, Shakeel Butt wrote: > > > On Mon, Jul 27, 2026 at 04:36:23PM +0200, Michal Hocko wrote: > > > > On Wed 22-07-26 17:19:07, Shakeel Butt wrote: > > > > [...] > > > > > > > > > > TBH I am not entirely happy about this approach. It effectivelly reverts > > > > a75ffa26122b ("memcg, oom: do not bypass oom killer for dying tasks"). > > > > It just makes it lockless. Assumption that a dying task will do so > > > > quickly and with bounded resources has turned wrong on several > > > > occasions. > > > > > > That's why I kept it as RFC :) > > > > > > > > > > > On the other hand I do undestand the contention issues and I can imagine > > > > that the existing solution doesn't really work well for huge thread > > > > groups that all end up lining up on the oom_lock just to learn there is > > > > nothing really killable anymore because they are the oom victim... > > > > > > > > Would it be just safer to bail out only for oom victim threads. This > > > > would narrow down potential runaways for oom victims which should be > > > > more limited than any killed/exiting task. It would also give the oom > > > > killer/reaper chance to work. WDYT? > > > > > > I will give the following patch a try with the reproducer I have. I am still > > > improving the reproducer as I am still not able to recreate multi hour slowdown > > > yet. I will report back once I have some results. > > > > > > > I have some results with the reproducer I (AI) wrote. > > > > Setup: 20k threads, each with its robust_list head on its own page in a > > large anon region pushed into a zswap pool (writeback off, so it's > > unreclaimable and pins the memcg at the limit). On the OOM-group-kill > > every thread faults that page in futex_cleanup() -> do_swap_page() -> > > swapin charge -> memcg OOM. A separate thread holds mmap_lock for write > > in a loop so the oom_reaper can't reap the pool -- matching the host, > > where the reaper was blocked and the memcg never fell below the limit. > > > > I tested on next-20260726 as baseline and then tested your suggestion over it. > > For baseline ~48k no-victim OOM invocations serialized on oom_lock; ~40s to > > drain the 20k threads in a VM (hours on the host, where each invocation > > was a dump_header over netconsole). With the patch the dying tasks stop > > entering out_of_memory and the storm is gone. > > > > With the following suggestion, the threads of dying tasks stop entering > > out_of_memory but the exit time doubled as each thread has to decompress the > > page from zswap. > > > > if (tsk_is_oom_victim(current)) > > goto force; > > > > I also tested by replacing goto force with goto nomem and the exit time halved > > i.e. ~20 seconds. Looking deeper it seems like each thread is still going > > through the reclaim loops. > > > > Just for testing purpose I moved this check along with goto nomem just before > > the reclaim fuction i.e. try_to_free_mem_cgroup_pages() and the exit time falls > > below 1 second. I think what we need is to detect early that the cgroup is > > unreclaimable and the threads of exiting/reaped process should just return with > > enomem. > > Do you mean, something like this? > --- > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 6dc4888a90f3..66f1eebf8c22 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -2648,6 +2648,18 @@ 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(current->signal->oom_mm)) I simply had tsk_is_oom_victim(current) check here. I assume you want MMF_OOM_REAP_QUEUED in the mm_flags_test() above. Do you want me to test with this additional mm_flags_test() as well? > + goto nomem; > + > __memcg_memory_event(mem_over_limit, MEMCG_MAX, allow_spinning); > raised_max_event = true; > > > -- > Michal Hocko > SUSE Labs