From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-170.mta1.migadu.com (out-170.mta1.migadu.com [95.215.58.170]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E08B33DB325 for ; Mon, 27 Jul 2026 20:49:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.170 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785185359; cv=none; b=XacaTSSHGUBJhRdAcz6tseCSUW8v+rvTV1PSBdp1yAlm6mI2rz2vvhs5ynqPdOfFl/OoCG9ikzMjKsvoDTO5Cy7HdaFUA09BP9OYYWpT+E8xc5N3/aUlT2FnV7/fNsmxuQLtzFxahOeNrFz+R4VcIWvCyAUCWG1BVhNNgMsM0I8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785185359; c=relaxed/simple; bh=wQXEPIFUBWXynVGrnaYEE4WP4cs09MsZYHtKqFIJKWY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=NrwVhBkjsf3sprZBUMQI1bg0eFjAPwvveatPvZ3YaA/OJ1yXf1WsV7VBT76BzCumNgQ/1jtx54KRcCfdhOywb3EdcC2pQrcTQtcDYPmrGkzCNxtpp7Q4IzUUNA1Zg5IWiEPNQbgdTL53xZAiI1ORYCcs7dfJ+N1kdRCoj62TCyw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=oFDB5P8n; arc=none smtp.client-ip=95.215.58.170 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="oFDB5P8n" Date: Mon, 27 Jul 2026 13:48:58 -0700 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1785185344; 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=FFvaZkohkm528INkbN+EO7pcO2PxXj1dIjGSZDzFMIg=; b=oFDB5P8n2pxOC9LeWJdqJfFQi0V+c/ConSiq6qsRnZqmzeEf4tmIRQU6+h264HoTbcAESP JH6T+IX8GwIpDwVJGCjZWMThhb13j4eD5V5MvQBTIXkee1+lh62bvAeV6NYlHP2ij1hc5g TfJmYfDldJRhnmE7pa1n2zDLdm9QByM= 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> Precedence: bulk X-Mailing-List: cgroups@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: X-Migadu-Flow: FLOW_OUT 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.