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 3658EC433EF for ; Wed, 27 Apr 2022 22:36:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233442AbiD0Wj3 (ORCPT ); Wed, 27 Apr 2022 18:39:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47472 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232266AbiD0Wj2 (ORCPT ); Wed, 27 Apr 2022 18:39:28 -0400 Received: from out1.migadu.com (out1.migadu.com [IPv6:2001:41d0:2:863f::]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 660CD6383; Wed, 27 Apr 2022 15:36:12 -0700 (PDT) Date: Wed, 27 Apr 2022 15:36:03 -0700 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1651098970; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=YptwFdA8KWuDmjvuchBNuhhYcNiTn83Pm656usmn0sI=; b=xurUMpP3QLqUoZxw1BdoFkYM+0wVMIHfRfnM/Miz+pyrSnam+pUfOqzeu4w7WEtz+vscdO t8sZhvk29FJHTf9oMznLUlDzxrKSBESrMWIxTbOsTmuGq6MX7UWPvgVN2r6Q4pckJigj3y prcDwZAQTSSNCJlRUCceBDukatZZNz4= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Roman Gushchin To: Vasily Averin Cc: Shakeel Butt , Michal =?iso-8859-1?Q?Koutn=FD?= , Vlastimil Babka , kernel@openvz.org, Florian Westphal , LKML , Michal Hocko , Cgroups , netdev , "David S. Miller" , Jakub Kicinski , Paolo Abeni Subject: Re: [PATCH memcg v4] net: set proper memcg for net_init hooks allocations Message-ID: References: <33085523-a8b9-1bf6-2726-f456f59015ef@openvz.org> <20220427122232.GA9823@blackbody.suse.cz> <6b18f82d-1950-b38e-f3f5-94f6c23f0edb@openvz.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <6b18f82d-1950-b38e-f3f5-94f6c23f0edb@openvz.org> X-Migadu-Flow: FLOW_OUT X-Migadu-Auth-User: linux.dev Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Thu, Apr 28, 2022 at 01:16:53AM +0300, Vasily Averin wrote: > On 4/27/22 18:06, Shakeel Butt wrote: > > On Wed, Apr 27, 2022 at 5:22 AM Michal Koutný wrote: > >> > >> On Tue, Apr 26, 2022 at 10:23:32PM -0700, Shakeel Butt wrote: > >>> [...] > >>>> > >>>> +static inline struct mem_cgroup *get_mem_cgroup_from_obj(void *p) > >>>> +{ > >>>> + struct mem_cgroup *memcg; > >>>> + > >>> > >>> Do we need memcg_kmem_enabled() check here or maybe > >>> mem_cgroup_from_obj() should be doing memcg_kmem_enabled() instead of > >>> mem_cgroup_disabled() as we can have "cgroup.memory=nokmem" boot > >>> param. > > Shakeel, unfortunately I'm not ready to answer this question right now. > I even did not noticed that memcg_kmem_enabled() and mem_cgroup_disabled() > have a different nature. > If you have no objections I'm going to keep this place as is and investigate > this question later. > > >> I reckon such a guard is on the charge side and readers should treat > >> NULL and root_mem_group equally. Or is there a case when these two are > >> different? > >> > >> (I can see it's different semantics when stored in current->active_memcg > >> (and active_memcg() getter) but for such "outer" callers like here it > >> seems equal.) > > Dear Michal, > I may have misunderstood your point of view, so let me explain my vision > in more detail. > I do not think that NULL and root_mem_cgroup are equal here: > - we have enabled cgroups and well-defined root_mem_cgroup, > - this function is called from inside memcg-limited container, > - we tried to get memcg from net, but without success, > and as result got NULL from mem_cgroup_from_obj() > (frankly speaking I do not think this situation is really possible) > If we keep memcg = NULL, then current's memcg will not be masked and > net_init's allocations will be accounted to current's memcg. > So we need to set active_memcg to root_mem_cgroup, it helps to avoid > incorrect accounting. It's way out of scope of this patch, but I think we need to stop using NULL as root_mem_cgroup/system scope indicator. Remaining use cases will be like end of cgroup iteration, active memcg not set, parent of the root memcg, etc. We can point root_mem_cgroup at a statically allocated structure on both CONFIG_MEMCG and !CONFIG_MEMCG. Does it sound reasonable or I'm missing some important points? Thanks!