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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5BDA1C433FE for ; Tue, 19 Oct 2021 06:30:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 40B3B61027 for ; Tue, 19 Oct 2021 06:30:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234262AbhJSGdA (ORCPT ); Tue, 19 Oct 2021 02:33:00 -0400 Received: from relay.sw.ru ([185.231.240.75]:36512 "EHLO relay.sw.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229755AbhJSGc5 (ORCPT ); Tue, 19 Oct 2021 02:32:57 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=virtuozzo.com; s=relay; h=Content-Type:MIME-Version:Date:Message-ID:From: Subject; bh=tI9gj9p8cg4CnX2QaPSuoyzqKweCoJS55yHjYE7xcKM=; b=is7WHUREKxBUK1eox a3i8e7lEICkLoC40q5DdZ9O1639miZT0QpjLzmTbey1KH61kzqfqNE46f3xVo3z+vEfv84cDtb3BC 5uvyqf7GIL1gRY7JUEs8Zy0etcbnAGPB4cxnlKeeFvMMW0HehqKkIbzMNocCK8KtCM4Z+5ti9g7d8 =; Received: from [172.29.1.17] by relay.sw.ru with esmtp (Exim 4.94.2) (envelope-from ) id 1mcie0-006Qqh-4l; Tue, 19 Oct 2021 09:30:40 +0300 Subject: Re: [PATCH memcg 0/1] false global OOM triggered by memcg-limited task To: Michal Hocko Cc: Johannes Weiner , Vladimir Davydov , Andrew Morton , Roman Gushchin , Uladzislau Rezki , Vlastimil Babka , Shakeel Butt , Mel Gorman , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel@openvz.org References: <9d10df01-0127-fb40-81c3-cc53c9733c3e@virtuozzo.com> <6b751abe-aa52-d1d8-2631-ec471975cc3a@virtuozzo.com> From: Vasily Averin Message-ID: <339ae4b5-6efd-8fc2-33f1-2eb3aee71cb2@virtuozzo.com> Date: Tue, 19 Oct 2021 09:30:18 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 18.10.2021 14:53, Michal Hocko wrote: > On Mon 18-10-21 13:05:35, Vasily Averin wrote: >> On 18.10.2021 12:04, Michal Hocko wrote: >>> On Mon 18-10-21 11:13:52, Vasily Averin wrote: >>> [...] >>>> How could this happen? >>>> >>>> User-space task inside the memcg-limited container generated a page fault, >>>> its handler do_user_addr_fault() called handle_mm_fault which could not >>>> allocate the page due to exceeding the memcg limit and returned VM_FAULT_OOM. >>>> Then do_user_addr_fault() called pagefault_out_of_memory() which executed >>>> out_of_memory() without set of memcg. >>>> >>>> Partially this problem depends on one of my recent patches, disabled unlimited >>>> memory allocation for dying tasks. However I think the problem can happen >>>> on non-killed tasks too, for example because of kmem limit. >>> >>> Could you be more specific on how this can happen without your patch? I >>> have to say I haven't realized this side effect when discussing it. >> If required I can try to search how try_charge_memcg() can reject page allocation >> of non-dying task too. > > Yes. Now I think that such failure was very unlikely (w/o my patch and kmem limit). I cannot exclude it completely, because I did not finished this review and perhaps I missed something, but I checked most part of code and found nothing. With my patch ("memcg: prohibit unconditional exceeding the limit of dying tasks") try_charge_memcg() can fail: a) due to fatal signal b) when mem_cgroup_oom -> mem_cgroup_out_of_memory -> out_of_memory() returns false (when select_bad_process() found nothing) To handle a) we can follow to your suggestion and skip excution of out_of_memory() in pagefault_out_of memory() To handle b) we can go to retry: if mem_cgroup_oom() return OOM_FAILED. However all these cases can be successfully handled by my new patch "memcg: prevent false global OOM triggered by memcg limited task" and I think it is better solution. Thank you, Vasily Averin