From mboxrd@z Thu Jan  1 00:00:00 1970
From: Waiman Long <longman-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Subject: Re: [PATCH v4 3/4] mm/page_owner: Print memcg information
Date: Mon, 7 Feb 2022 14:33:57 -0500
Message-ID: <53f89ef2-3894-ad23-7484-38ce192bce20@redhat.com>
References: <20220131192308.608837-5-longman@redhat.com>
 <20220202203036.744010-4-longman@redhat.com>
 <YfvOp5VXrxy9IW1w@dhcp22.suse.cz>
 <3f042edb-3769-afea-17a7-899578cd5c69@redhat.com>
 <YgFUxFI5bMbc42j4@dhcp22.suse.cz>
 <20220207110947.f07b58898d91c02090f9aacf@linux-foundation.org>
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Return-path: <cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com;
        s=mimecast20190719; t=1644262451;
        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=Mt0dY24O8oy81HO9eljR8ZyBXQGPacTP1E1VhcVXUbE=;
        b=gZBkxxMJizo3mPCjQT6YvqGdeTOzA7uAmfYRANSXAsOMj0gATDhucQSGsHRYkuxUqLaP1w
        YHoPGae+RVQnq5mhxM3QWWCh/fFuzoQLpjDetw59EmWq6mNms+9UJT9rxi6qUfgUo0CjIr
        GKR11xdo1r8HBzpYWVtQFA+dl9hC50w=
Content-Language: en-US
In-Reply-To: <20220207110947.f07b58898d91c02090f9aacf-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>
List-ID: <cgroups.vger.kernel.org>
Content-Type: text/plain; charset="us-ascii"; format="flowed"
To: Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, Michal Hocko <mhocko-IBi9RG/b67k@public.gmane.org>
Cc: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>, Vladimir Davydov <vdavydov.dev-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, Petr Mladek <pmladek-IBi9RG/b67k@public.gmane.org>, Steven Rostedt <rostedt-nx8X9YLhiw1AfugRpC6u6w@public.gmane.org>, Sergey Senozhatsky <senozhatsky-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>, Andy Shevchenko <andriy.shevchenko-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>, Rasmus Villemoes <linux-qQsb+v5E8BnlAoU/VqSP6n9LOBIZ5rWg@public.gmane.org>, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, Ira Weiny <ira.weiny-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>, Mike Rapoport <rppt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, David Rientjes <rientjes-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, Roman Gushchin <guro-b10kYP2dOMg@public.gmane.org>, Rafael Aquini <aquini-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>


On 2/7/22 14:09, Andrew Morton wrote:
> On Mon, 7 Feb 2022 18:20:04 +0100 Michal Hocko <mhocko-IBi9RG/b67k@public.gmane.org> wrote:
>
>> On Thu 03-02-22 14:03:58, Waiman Long wrote:
>>> On 2/3/22 07:46, Michal Hocko wrote:
>>>> On Wed 02-02-22 15:30:35, Waiman Long wrote:
>>>> [...]
>> ...
>>>>> +	online = (memcg->css.flags & CSS_ONLINE);
>>>>> +	cgroup_name(memcg->css.cgroup, name, sizeof(name));
>>>> Is there any specific reason to use another buffer allocated on the
>>>> stack? Also 80B seems too short to cover NAME_MAX.
>>>>
>>>> Nothing else jumped at me.
>>> I suppose we can print directly into kbuf with cgroup_name(), but using a
>>> separate buffer is easier to read and understand. 79 characters should be
>>> enough for most cgroup names. Some auto-generated names with some kind of
>>> embedded uuids may be longer than that, but the random sequence of hex
>>> digits that may be missing do not convey much information for identification
>>> purpose. We can always increase the buffer length later if it turns out to
>>> be an issue.
>> Cutting a name short sounds like a source of confusion and there doesn't
>> seem to be any good reason for that.
> Yes.  If we give them 79 characters, someone will go and want 94.  If
> we can prevent this once and for ever, let's please do so.

Sure. Will send a version with that change.

Cheers,
Longman

>