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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 52AA6C43334 for ; Mon, 6 Jun 2022 08:33:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231734AbiFFIdk (ORCPT ); Mon, 6 Jun 2022 04:33:40 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47938 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231731AbiFFIdc (ORCPT ); Mon, 6 Jun 2022 04:33:32 -0400 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 358E02FE66 for ; Mon, 6 Jun 2022 01:33:31 -0700 (PDT) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out2.suse.de (Postfix) with ESMTP id EF1B71F461; Mon, 6 Jun 2022 08:33:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1654504409; h=from:from:reply-to: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=WJjaloV5+HcQZaXHw0f2gF+Srokd4wPErX0W6s9DSTk=; b=mr9DatIXY6/NaJHuzz/M8tzq7pvqO1aylMjVb+LQFp0SlIoyDdjNP1/7i7x1eLDZMlqveD hJQjB4y6xBUBvJ5hX2QDSZALFiamLe5HLZjUBK3zoM6V9aj8AhDSKcIvJetIUGnTGRtEug iUfDMtu0S96uvVi+kFbXG/aA+8WP6uE= Received: from suse.cz (unknown [10.100.201.86]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id AE1082C141; Mon, 6 Jun 2022 08:33:29 +0000 (UTC) Date: Mon, 6 Jun 2022 10:33:29 +0200 From: Michal Hocko To: Zackary Liu Cc: "akpm@linux-foundation.org" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] mm/oom_kill: break evaluation when a task has been selected Message-ID: References: <6BC32F66-2AC4-450D-90D5-B7A09455B617@getmailspring.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6BC32F66-2AC4-450D-90D5-B7A09455B617@getmailspring.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat 04-06-22 18:35:19, Zackary Liu wrote: > > On Jun 1 2022, at 3:45 pm, Michal Hocko wrote: > > > On Sat 14-05-22 15:52:28, Zhaoyu Liu wrote: > >> oom points no longer need to be calculated if a task is oom_task_origin(), > >> so return 1 to stop the oom_evaluate_task(). > > > > This doesn't really explain why this is really desired. Is this a fix, > > optimization? > > > > Please also note that this change has some side effects. For one, the > > task marked as oom origin will get killed even if there is still a > > pending oom victim which hasn't been fully dismantled. Is this > > intentional? > > Thank you very much for reminding. > > From my point of view, the victim was marked in the last oom, and now it > has entered the oom again, which means that the system still has no > deprecated memory available. This is not an unusual situation. OOM victims can take some time to die and release their memory. The oom_reaper is there to fast forward that process and guarantee a forward progress. But this can still take some time. Our general policy is to back off when there is an alive oom victim encountered. Have a look at the tsk_is_oom_victim test in oom_evaluate_task. For that heuristic to be effective the whole task list (wether the global one or memcg) has to be evaluated. > In order to ensure that the system can > return to normal as soon as possible, killing the origin task > immediately should be A good choice, and the role of this patch is to > end oom_evaluate_task and return true as soon as the origin task is found. Could you be more specific how does this patch guarantees a forward progress? What is the actual usecase that benefits from this change? These are all important information for future reference. Please note I am not saying the patch is wrong. I just still do not see why it is useful. > Maybe this patch is not the optimal solution, it has a trade-off. If there are trade-offs, please document them in the changelog. The way I see it is that oom_task_origin heuristic has been introduced to help killing swapoff operation because the swapped out memory doesn't fit into memory. This is a very reasonable thing to do in general but it also represents an early failure visible to the userspace. If there is a pre-existing oom victim then I would argue that we should try to avoid the failure. -- Michal Hocko SUSE Labs