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 9DC4AC433FE for ; Wed, 2 Feb 2022 16:38:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345912AbiBBQiL (ORCPT ); Wed, 2 Feb 2022 11:38:11 -0500 Received: from smtp-out1.suse.de ([195.135.220.28]:56236 "EHLO smtp-out1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234678AbiBBQiJ (ORCPT ); Wed, 2 Feb 2022 11:38:09 -0500 Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out1.suse.de (Postfix) with ESMTP id 2941721100; Wed, 2 Feb 2022 16:38:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1643819888; 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=ovtEFN3zyuhZ84VATTXxeaX4XxbwY8ky/fQzl6DC/1E=; b=VbieOmiRhqEU6RioiXSYtTXq1pkpEM59XXP4jKGogGC6DPO62BFtWfjW0oxah/XnG4ZUpr fVcilnkkpeLfnCDqL24v6MCv/f+OzRTkaH1XJ7IPGKFxSvII98y0Pztp7ZHSXVDOgIndiB B908vNICOfe2bWd7yPqAP6oCJuqr0bA= 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 98642A3B8E; Wed, 2 Feb 2022 16:38:07 +0000 (UTC) Date: Wed, 2 Feb 2022 17:38:07 +0100 From: Michal Hocko To: Roman Gushchin Cc: Waiman Long , Johannes Weiner , Vladimir Davydov , Andrew Morton , Petr Mladek , Steven Rostedt , Sergey Senozhatsky , Andy Shevchenko , Rasmus Villemoes , linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org, Ira Weiny , Rafael Aquini Subject: Re: [PATCH v2 3/3] mm/page_owner: Dump memcg information Message-ID: References: <20220129205315.478628-4-longman@redhat.com> <12686956-612d-d89b-5641-470d5e913090@redhat.com> <268a8bdf-4c70-b967-f34c-2293b54186f0@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 02-02-22 07:54:48, Roman Gushchin wrote: > On Wed, Feb 02, 2022 at 09:57:18AM +0100, Michal Hocko wrote: > > On Tue 01-02-22 11:41:19, Waiman Long wrote: > > > > > > On 2/1/22 05:49, Michal Hocko wrote: > > [...] > > > > Could you be more specific? Offlined memcgs are still part of the > > > > hierarchy IIRC. So it shouldn't be much more than iterating the whole > > > > cgroup tree and collect interesting data about dead cgroups. > > > > > > What I mean is that without piggybacking on top of page_owner, we will to > > > add a lot more code to collect and display those information which may have > > > some overhead of its own. > > > > Yes, there is nothing like a free lunch. Page owner is certainly a tool > > that can be used. My main concern is that this tool doesn't really > > scale on large machines with a lots of memory. It will provide a very > > detailed information but I am not sure this is particularly helpful to > > most admins (why should people process tons of allocation backtraces in > > the first place). Wouldn't it be sufficient to have per dead memcg stats > > to see where the memory sits? > > > > Accumulated offline memcgs is something that bothers more people and I > > am really wondering whether we can do more for those people to evaluate > > the current state. > > Cgroup v2 has corresponding counters for years. Or do you mean something different? Do we have anything more specific than nr_dying_descendants? I was thinking about an interface which would provide paths and stats for dead memcgs. But I have to confess I haven't really spent much time thinking about how much work that would be. I am by no means against adding memcg information to the page owner. I just think there must be a better way to present resource consumption by dead memcgs. -- Michal Hocko SUSE Labs