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 A08CE19DF6C for ; Tue, 9 Jul 2024 16:09:14 +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=1720541356; cv=none; b=Q1pKsNWh2lUp1ISLYzR7HUWxKHkez+LM29sEPDpaxQjR8yGrT1R5746MMNYmqg4gn+dzKEhpvSQLy4qr6dPdTkB9SY6qWTJ0ZMCYj5AcHQQDZ00fokuiQH6tDTOwmcv6cz/DEbpMycYGLK6o4LiJyw4tL+UWpE1sR39idO9kQHw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1720541356; c=relaxed/simple; bh=FGRnS6HrOy8B60pAUYJYvZ43kcQMTlUlioArToOkYZA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=LroJSrmNGbhTjF3WJL7ICQsmFzB1h2zpznXUKjzCgYaDgSZr0mfcdlYTr2WVbddntVt8oavs1r8RnDgKIfXa3fHYx8wZiwcr/srO9kQBLMkZLFhlpdySuZAncE24YfpNNmgMnUcTNZ3E4pxlRedOLxeWmoxu/zjtuD3zm+5kGP8= 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=Ldo0q05F; 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="Ldo0q05F" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1720541353; 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=zsIWbJCIxtXdUtyfcJ/HuCRS5/rhV3Z8dkkrqoWXNu8=; b=Ldo0q05F8PW/QjPLAM848yySfL5SECgOAgll6rkSWdLe5Th42kLMCpPTX9NiA5mJZ55uQl OpZj76kGs81kbGnMQ8u+VabQ+sDWrM/h6kGODZrqLmSVHQwK2EscH5cR79h9VcJjYUAt/M C9w79xgB3TXnx57f5RS3X3EjY8XYvtk= Received: from mx-prod-mc-05.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-15-PxWcNCzsPEK7IR4Uy1xlTg-1; Tue, 09 Jul 2024 12:09:10 -0400 X-MC-Unique: PxWcNCzsPEK7IR4Uy1xlTg-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-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 40AFE1955F67; Tue, 9 Jul 2024 16:09:08 +0000 (UTC) Received: from [10.22.34.7] (unknown [10.22.34.7]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 29E8C3000181; Tue, 9 Jul 2024 16:09:05 +0000 (UTC) Message-ID: <4291c0ed-bc37-46de-b081-271e8b299b1d@redhat.com> Date: Tue, 9 Jul 2024 12:09:05 -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: Kamalesh Babulal , Tejun Heo , Zefan Li , Johannes Weiner , Jonathan Corbet Cc: 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> Content-Language: en-US From: Waiman Long In-Reply-To: <1c0d9ee1-e80a-46da-a48d-2ab23dd04673@oracle.com> 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 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. Cheers, Longman