linux-kernel - Re: [PATCH v4 4/4] mm/page_owner: Record task command name

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Date:   Wed, 2 Feb 2022 11:53:52 -0500
From:   Waiman Long <longman@...hat.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        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>,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH v4 4/4] mm/page_owner: Record task command name


On 2/1/22 10:28, Michal Hocko wrote:
> Cc Vlastimil
>
> On Mon 31-01-22 17:03:28, Waiman Long wrote:
>> The page_owner information currently includes the pid of the calling
>> task. That is useful as long as the task is still running. Otherwise,
>> the number is meaningless. To have more information about the allocating
>> tasks that had exited by the time the page_owner information is
>> retrieved, we need to store the command name of the task.
>>
>> Add a new comm field into page_owner structure to store the command name
>> and display it when the page_owner information is retrieved.
> I completely agree that pid is effectivelly useless (if not misleading)
> but is comm really telling all that much to compensate for the
> additional storage required for _each_ page in the system?

Yes, it does add an extra 16 bytes per page overhead. The command name 
can be useful if one want to find out which userspace command is 
responsible for a problematic page allocation. Maybe we can remove pid 
from page_owner to save 8 bytes as you also agree that this number is 
not that useful.

Cheers,
Longman