linux-kernel - Re: [PATCH v4 3/4] mm/page_owner: Print memcg information

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Message-ID: <53f89ef2-3894-ad23-7484-38ce192bce20@redhat.com>
Date:   Mon, 7 Feb 2022 14:33:57 -0500
From:   Waiman Long <longman@...hat.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
        linux-mm@...ck.org, Ira Weiny <ira.weiny@...el.com>,
        Mike Rapoport <rppt@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Roman Gushchin <guro@...com>, Rafael Aquini <aquini@...hat.com>
Subject: Re: [PATCH v4 3/4] mm/page_owner: Print memcg information


On 2/7/22 14:09, Andrew Morton wrote:
> On Mon, 7 Feb 2022 18:20:04 +0100 Michal Hocko <mhocko@...e.com> 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

>