From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wr1-f52.google.com (mail-wr1-f52.google.com [209.85.221.52]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D047439CCF3 for ; Tue, 28 Jul 2026 19:23:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.221.52 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785266627; cv=none; b=rZxPFlHsrmioS0JHFBJIE9Dr3pCpARp9u7vqAqTz/rkmb0BrYSAHUBnNiWGAhZTNGGbzNEM+VajnOXr+45wxwPid4bqZSt0FnLzLvuU3FXHGWflLx0PIvq7M/DaFE1Eg7SvkBI/9Z9RFV8q2wbMqdXwbrgV1HXSLPuOuvAaJjnA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785266627; c=relaxed/simple; bh=pBhHjY4lmyfN+zGiDNSUsLHi2xqfgYzXS+aNGMlJq9k=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=eJSMrzp9iKAF4bzCeKnCRrdvRZbdj1UnBOhBLNAdUb4FzlN4iztQdcHWk6DwGzxGU2R107mT95Q+ihoa9+XuCh4bYb7TZ/m1G3g6b5NgGtXHYrp4bK8DQSgpuC3QZUJOjpylG4MdJsidZR1C/s0wBlRzGUOfPHkc0B99SSIZn4k= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=suse.com; spf=pass smtp.mailfrom=suse.com; dkim=pass (2048-bit key) header.d=suse.com header.i=@suse.com header.b=IK6oJ86Z; arc=none smtp.client-ip=209.85.221.52 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=suse.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=suse.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=suse.com header.i=@suse.com header.b="IK6oJ86Z" Received: by mail-wr1-f52.google.com with SMTP id ffacd0b85a97d-471eeac43bfso197207f8f.3 for ; Tue, 28 Jul 2026 12:23:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=google; t=1785266623; x=1785871423; darn=vger.kernel.org; h=in-reply-to:content-disposition:content-type:mime-version :references:message-id:subject:cc:to:from:date:from:to:cc:subject :date:message-id:reply-to:content-type; bh=K8qZfjaxhGbSgiZnpnKGN1HzCLFjiwC8FeQ/0VidGnU=; b=IK6oJ86ZF9qx1GtzaORjQ2Iuhjxr1H3CHcXzxrFiKtMDuRaDwyUVvb6fb28VXLSn84 RpjgUc93e1t3Y3vEJjCKB9wWolGMT1hPuEoUBF7p0FH2OTAoOwH21b4+YLAu7kpOGx6H 9Jy1EDVImq+CwJTeciiv5G6JOCiFATmWPPDQ7/WL8LwdDMaL4w57+dgIJ/YIylCR0Fsi wzo4Ul/PrOkybMB7WfI31f9hOliD/3OPbBo49dyjswbnyGaStmrqcP7ogC5bsEOBEr1e i71CrGZH1oXxUQfweZCu2xC4xAH8s5AT6N7DcZf9DXo4RR8/e/DIXTBtx5EsGqKqqxJ4 090g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1785266623; x=1785871423; h=in-reply-to:content-disposition:content-type:mime-version :references:message-id:subject:cc:to:from:date:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=K8qZfjaxhGbSgiZnpnKGN1HzCLFjiwC8FeQ/0VidGnU=; b=WYjk+R8uTPBtnAckLvzsWkejH3xwc88fEoh33Mw/z6IWHNqJtYjvWfakMGXj2iP5Ul H5PZuQOkj/2i5v8PVryXuAyzQda+q8iFS7UQRpF9dDeEuMdKLnIfwgzm3TStNKfbbfF8 CJ1vRscB2JF8EMZmyLKkiXcC0Qs3CtmUNTovhkHWv/YP6hiI3TN9Hb+KQ/EmIeYpYH/h hpuxv/GtNWMbvfqfuj0pyExbRNinKkZWxQDWb+jULs2hd+mDpXgOqCE79kOyvcm0T/mt knfGz8wOt3u8RMQ4PqcnEvG8MrNUBQZdb0XRdpcXnJ3JDvw5vwRZwryKN1kzwjf3w0t4 AzwQ== X-Forwarded-Encrypted: i=1; AHgh+RrwchcKDE5ea/f54iYZAkAycX/mLs7AamCIA5SMlNLtCUbs9x8IaXj5w2/jW42xh/abtsnjqvYe@vger.kernel.org X-Gm-Message-State: AOJu0Yz7IlpOCXtw/yn9DzJaZ/U0Qtd+ZTb+dsFNspWIkmGi7JcLVxCJ i+GOYXWC12EUHFALt7daaYJ8CKgw7BGqDu6T49zbN9/6n9/CXcWv4tEqeyhPoPQ0tBU= X-Gm-Gg: AR+sD11j57y+ny7cm2JWI1ATT3PSdV00XLiOY25vJ7zqrcykKfZTAzXJ4uSW3Jxjlqv sD6dnAKnbKqo1ZLrDwbRTuzGSclksD7gbJM8NZ8bwAjwPy+YxXRhukIvU9p6K6lBpsgelaIyvhN qcKizTRTXG2hU7FI+KbxlcUiHB8TY8dPD/n7rYnIgj+5t5VWpy2qqDXEC4dWaD/qGAdOc2LeVg1 /koomxyrr0chOztOcKQPJCXw3AE0EZ/iL+NiGC7QM86WXJslPWrreEo42kzDjQ9gZdkz+twarIg 6ByP/bB3IrhmKHb7lzpkvyDSmKM000hr2qp2gk83fiUDNBkBcSuoqyS5/j3ceROr1TqLooyXYkk 34R6Mlyy7A2w3WRKQBfVTCp0J+fBvZLex5sdwxojYCwaS6u46eUTsPIeL0OGVuv6J8bmXSUejHv EmojNhgQFWSzs61XuzY9U+knD6G35xyOto9HtMfY3dMBvOwcU7ssoOkFx3d+JcQD3QvIgd X-Received: by 2002:a5d:5849:0:b0:47f:8f8f:e494 with SMTP id ffacd0b85a97d-47fb1ec88d4mr4116620f8f.2.1785266622998; Tue, 28 Jul 2026 12:23:42 -0700 (PDT) Received: from localhost (109-81-83-7.rct.o2.cz. [109.81.83.7]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-47fb6b189fbsm1268107f8f.25.2026.07.28.12.23.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 28 Jul 2026 12:23:42 -0700 (PDT) Date: Tue, 28 Jul 2026 21:23:41 +0200 From: Michal Hocko To: Shakeel Butt 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 , =?iso-8859-1?Q?Andr=E9?= 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: On Tue 28-07-26 09:55:21, Shakeel Butt wrote: > 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 was hoping for a more specific treatment. > 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? Sorry I meant MMF_OOM_SKIP there. -- Michal Hocko SUSE Labs