From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DBD43195FD5 for ; Wed, 10 Jul 2024 18:28:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1720636117; cv=none; b=tDl07wI93ixC8VH04ppv1yKlphI8Er5IUN9VzsIujoDQB85gle3+iRvEKOc2p6Hi4EsuO2BVx7uEuyDZNfyTPbCvUzbTwoylLzyMwuZjPhiFQ3wePwJ5kMrkbyPApgKvdkOQAi1RupO6wTniwJD3Z5dIEJelW+9iwOc21iQtSog= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1720636117; c=relaxed/simple; bh=ZVpVZPoW5DhjzOavrR5GY0hpK7EfHLGxovPutWlyOEU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Z2Pd6tew45oX4Pzp0LRS9v4202O+oG7rCyaaFeK0amldsojVhnITYXtjhfbSWNh48dgVOTS6+NBrenh7cRgrBO1Omm4kV4xALaJr77NKx8NZMxjWJy0R3cnLIGmQUD6YOnWXeb9+Ln4tqKbStyDt9s9Koa7ExVJiRnooMLsCPR8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=YrdI4Dx5; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="YrdI4Dx5" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1720636114; 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=qF8mAtiIKc1hNwFwVQgDd+xtcEIQ7/hxF8mGp9dv70U=; b=YrdI4Dx5F9dXZMZHUXxcVE7ZjTTn4EPphi7Ers9DSnPV6qDxr8UJmTbzHQb0kwWVV26gDK xk/HsgNQP4cRs4PycC7SRnkiX3YYswFscAebvmZO/atqy3W65bzZl3djv1NjFXRVQFBlNZ jHEOneMsc04dKFhSLeCU7j8pEf51ZZg= Received: from mx-prod-mc-04.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-347-kjVYtQYOOeyYt79GQJew1g-1; Wed, 10 Jul 2024 14:28:30 -0400 X-MC-Unique: kjVYtQYOOeyYt79GQJew1g-1 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 7C03519560BF; Wed, 10 Jul 2024 18:28:27 +0000 (UTC) Received: from [10.22.48.10] (unknown [10.22.48.10]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 93A2D3000181; Wed, 10 Jul 2024 18:28:25 +0000 (UTC) Message-ID: Date: Wed, 10 Jul 2024 14:28:24 -0400 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH-cgroup v2] cgroup: Show # of subsystem CSSes in root cgroup.stat To: Johannes Weiner Cc: Kamalesh Babulal , Tejun Heo , Zefan Li , Jonathan Corbet , cgroups@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org References: <20240709132814.2198740-1-longman@redhat.com> <1c0d9ee1-e80a-46da-a48d-2ab23dd04673@oracle.com> <4291c0ed-bc37-46de-b081-271e8b299b1d@redhat.com> <20240709180231.GA251628@cmpxchg.org> Content-Language: en-US From: Waiman Long In-Reply-To: <20240709180231.GA251628@cmpxchg.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 On 7/9/24 14:02, Johannes Weiner wrote: > On Tue, Jul 09, 2024 at 12:09:05PM -0400, Waiman Long wrote: >> On 7/9/24 11:58, Kamalesh Babulal wrote: >>> On 7/9/24 6:58 PM, Waiman Long wrote: >>>> The /proc/cgroups file shows the number of cgroups for each of the >>>> subsystems. With cgroup v1, the number of CSSes is the same as the >>>> number of cgroups. That is not the case anymore with cgroup v2. The >>>> /proc/cgroups file cannot show the actual number of CSSes for the >>>> subsystems that are bound to cgroup v2. >>>> >>>> So if a v2 cgroup subsystem is leaking cgroups (usually memory cgroup), >>>> we can't tell by looking at /proc/cgroups which cgroup subsystems may be >>>> responsible. This patch adds CSS counts in the cgroup_subsys structure >>>> to keep track of the number of CSSes for each of the cgroup subsystems. >>>> >>>> As cgroup v2 had deprecated the use of /proc/cgroups, the root >>>> cgroup.stat file is extended to show the number of outstanding CSSes >>>> associated with all the non-inhibited cgroup subsystems that have been >>>> bound to cgroup v2. This will help us pinpoint which subsystems may be >>>> responsible for the increasing number of dying (nr_dying_descendants) >>>> cgroups. >>>> >>>> The cgroup-v2.rst file is updated to discuss this new behavior. >>>> >>>> With this patch applied, a sample output from root cgroup.stat file >>>> was shown below. >>>> >>>> nr_descendants 53 >>>> nr_dying_descendants 34 >>>> nr_cpuset 1 >>>> nr_cpu 40 >>>> nr_io 40 >>>> nr_memory 87 >>>> nr_perf_event 54 >>>> nr_hugetlb 1 >>>> nr_pids 53 >>>> nr_rdma 1 >>>> nr_misc 1 >>>> >>>> In this particular case, it can be seen that memory cgroup is the most >>>> likely culprit for causing the 34 dying cgroups. >>>> >>>> Signed-off-by: Waiman Long >>>> --- >>>> Documentation/admin-guide/cgroup-v2.rst | 10 ++++++++-- >>>> include/linux/cgroup-defs.h | 3 +++ >>>> kernel/cgroup/cgroup.c | 19 +++++++++++++++++++ >>>> 3 files changed, 30 insertions(+), 2 deletions(-) >>>> >>>> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst >>>> index 52763d6b2919..65af2f30196f 100644 >>>> --- a/Documentation/admin-guide/cgroup-v2.rst >>>> +++ b/Documentation/admin-guide/cgroup-v2.rst >>>> @@ -981,6 +981,12 @@ All cgroup core files are prefixed with "cgroup." >>>> A dying cgroup can consume system resources not exceeding >>>> limits, which were active at the moment of cgroup deletion. >>>> >>>> + nr_ >>>> + Total number of cgroups associated with that cgroup >>>> + subsystem, e.g. cpuset or memory. These cgroup counts >>>> + will only be shown in the root cgroup and for subsystems >>>> + bound to cgroup v2. >>>> + >>>> cgroup.freeze >>>> A read-write single value file which exists on non-root cgroups. >>>> Allowed values are "0" and "1". The default is "0". >>>> @@ -2930,8 +2936,8 @@ Deprecated v1 Core Features >>>> >>>> - "cgroup.clone_children" is removed. >>>> >>>> -- /proc/cgroups is meaningless for v2. Use "cgroup.controllers" file >>>> - at the root instead. >>>> +- /proc/cgroups is meaningless for v2. Use "cgroup.controllers" or >>>> + "cgroup.stat" files at the root instead. >>>> >>>> >>>> Issues with v1 and Rationales for v2 >>>> diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h >>>> index b36690ca0d3f..522ab77f0406 100644 >>>> --- a/include/linux/cgroup-defs.h >>>> +++ b/include/linux/cgroup-defs.h >>>> @@ -776,6 +776,9 @@ struct cgroup_subsys { >>>> * specifies the mask of subsystems that this one depends on. >>>> */ >>>> unsigned int depends_on; >>>> + >>>> + /* Number of CSSes, used only for /proc/cgroups */ >>>> + atomic_t nr_csses; >>>> }; >>>> >>>> extern struct percpu_rw_semaphore cgroup_threadgroup_rwsem; >>>> diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c >>>> index c8e4b62b436a..48eba2737b1a 100644 >>>> --- a/kernel/cgroup/cgroup.c >>>> +++ b/kernel/cgroup/cgroup.c >>>> @@ -3669,12 +3669,27 @@ static int cgroup_events_show(struct seq_file *seq, void *v) >>>> static int cgroup_stat_show(struct seq_file *seq, void *v) >>>> { >>>> struct cgroup *cgroup = seq_css(seq)->cgroup; >>>> + struct cgroup_subsys *ss; >>>> + int i; >>>> >>>> seq_printf(seq, "nr_descendants %d\n", >>>> cgroup->nr_descendants); >>>> seq_printf(seq, "nr_dying_descendants %d\n", >>>> cgroup->nr_dying_descendants); >>>> >>>> + if (cgroup_parent(cgroup)) >>>> + return 0; >>>> + >>>> + /* >>>> + * For the root cgroup, shows the number of csses associated >>>> + * with each of non-inhibited cgroup subsystems bound to it. >>>> + */ >>>> + do_each_subsys_mask(ss, i, ~cgrp_dfl_inhibit_ss_mask) { >>>> + if (ss->root != &cgrp_dfl_root) >>>> + continue; >>>> + seq_printf(seq, "nr_%s %d\n", ss->name, >>>> + atomic_read(&ss->nr_csses)); >>>> + } while_each_subsys_mask(); >>>> return 0; >>>> } >>>> >>> Thanks for adding nr_csses, the patch looks good to me. A preference comment, >>> nr__css format, makes it easier to interpret the count. >>> >>> With or without the changes to the cgroup subsys format: >>> >>> Reviewed-by: Kamalesh Babulal >> Thanks for the review. >> >> CSS is a kernel internal name for cgroup subsystem state. Non kernel >> developers or users may not know what CSS is and cgroup-v2.rst doesn't >> mention CSS at all. So I don't think it is a good idea to add the "_css" >> suffix. From the user point of view, the proper term to use here is the >> number of cgroups, just like what "nr_descendants" and >> "nr_dying_descendants" are referring to before this patch. The only >> issue that I didn't address is the use of the proper plural form which >> is hard for cgroup subsystem names that we have. > It's not quite the same right? You could have 1 dying cgroup with > multiple zombie subsys states. At least in theory. It could be > confusing to add these counts without introducing the css concept. > > I also wonder if it would be better to just report the dying css > instead of all of them. Live ones are 1) under user control and 2) > easy to inspect in cgroupfs. I can see a scenario for the > nr_descendants aggregation ("Oh, that's a lot of subgroups!"); and a > scenario for dying css ("Oh, it's memory state pinning dead groups!"). > But not so much "Oh, that's a lot of live memory controlled groups!" > > I can't think of a good name for it though. > > nr_dying_memory_css is a mouthful > > nr_offline_memory? > > nr_zombie_memory? > > Should this be in debugfs? > I just have sent out a v3 patch that make this hierarchical and separate out live and dying csses. Let me know if you have other suggestions. Thanks, Longman