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 X-Spam-Level: X-Spam-Status: No, score=-14.2 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E909EC433EF for ; Mon, 13 Sep 2021 09:38:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D1B0861004 for ; Mon, 13 Sep 2021 09:38:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238741AbhIMJjR (ORCPT ); Mon, 13 Sep 2021 05:39:17 -0400 Received: from relay.sw.ru ([185.231.240.75]:36190 "EHLO relay.sw.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238675AbhIMJjQ (ORCPT ); Mon, 13 Sep 2021 05:39:16 -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=TkHNL+ib7NjPWsL57OO6zVdK+l/V7nLiS/zl/t9RNEE=; b=mJMKaH5Pr/TTWXM+k BEesbC+Nhe8eaboiOWdPHcU5U96lxPEXpN9qBs6mIIhOBWJukn/dMrao3+jSik9NoiDCJ433lNL1D iFTCZhUdXvw3FbwiTF/L4rZS0qQBqAMcRAEKv7t/zgTypsrXOeHh8j3HVW0/bYC89sjznMxIt5Pyg =; Received: from [10.93.0.56] by relay.sw.ru with esmtp (Exim 4.94.2) (envelope-from ) id 1mPiPV-001nw1-Lj; Mon, 13 Sep 2021 12:37:57 +0300 Subject: Re: [PATCH memcg] memcg: prohibit unconditional exceeding the limit of dying tasks To: Michal Hocko Cc: Johannes Weiner , Vladimir Davydov , Andrew Morton , Tetsuo Handa , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <5b06a490-55bc-a6a0-6c85-690254f86fad@virtuozzo.com> <8b98d44a-aeb2-5f5f-2545-ac2bd0c7049b@virtuozzo.com> From: Vasily Averin Message-ID: Date: Mon, 13 Sep 2021 12:37:56 +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 9/13/21 11:39 AM, Michal Hocko wrote: > On Mon 13-09-21 10:51:37, Vasily Averin wrote: >> On 9/10/21 3:39 PM, Vasily Averin wrote: >>> The kernel currently allows dying tasks to exceed the memcg limits. >>> The allocation is expected to be the last one and the occupied memory >>> will be freed soon. >>> This is not always true because it can be part of the huge vmalloc >>> allocation. Allowed once, they will repeat over and over again. >> >>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c >>> index 389b5766e74f..67195fcfbddf 100644 >>> --- a/mm/memcontrol.c >>> +++ b/mm/memcontrol.c >>> @@ -2622,15 +2625,6 @@ static int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask, >>> if (gfp_mask & __GFP_ATOMIC) >>> goto force; >>> >>> - /* >>> - * Unlike in global OOM situations, memcg is not in a physical >>> - * memory shortage. Allow dying and OOM-killed tasks to >>> - * bypass the last charges so that they can exit quickly and >>> - * free their memory. >>> - */ >>> - if (unlikely(should_force_charge())) >>> - goto force; >>> - >> >> Should we keep current behaviour for (current->flags & PF_EXITING) case perhaps? > > Why? On this stage task really dies and mostly releases taken resources. It can allocate though, and this allocation can reach memcg limit due to the activity of parallel memcg threads. Noting bad should happen if we reject this allocation, because the same thing can happen in non-memcg case too. However I doubt misuse is possible here and we have possibility to allow graceful shutdown here. In other words: we are not obliged to allow such allocations, but we CAN do it because we hope that it is safe and cannot be misused. >> It is set inside do_exit only and (I hope) cannot trigger huge vmalloc allocations. > > Allocations in this code path should be rare but it is not like they are > non-existent. This is rather hard to review area spread at many places > so if we are deciding to make the existing model simpler (no bypassing) > then I would rather have no exceptions unless they are reaaly necessary > and document them if they are. Thank you, vasily Averin