linux-kernel - Re: [PATCH v3 4/4] mm/page_owner: Record task command name

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Date:   Mon, 31 Jan 2022 16:46:27 -0500
From:   Waiman Long <longman@...hat.com>
To:     Roman Gushchin <guro@...com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.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>,
        Rafael Aquini <aquini@...hat.com>
Subject: Re: [PATCH v3 4/4] mm/page_owner: Record task command name

On 1/31/22 15:54, Roman Gushchin wrote:
> On Mon, Jan 31, 2022 at 02:23:08PM -0500, 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. Only the
>> first 15 characters of the command name will be copied, but that should
>> be enough in most cases. Even for those commands with longer names,
>> it shouldn't be hard to guess what they are.
>>
>> Signed-off-by: Waiman Long <longman@...hat.com>
>> ---
>>   mm/page_owner.c | 16 ++++++++++++----
>>   1 file changed, 12 insertions(+), 4 deletions(-)
>>
>> diff --git a/mm/page_owner.c b/mm/page_owner.c
>> index a471c74c7fe0..8b2b381fd986 100644
>> --- a/mm/page_owner.c
>> +++ b/mm/page_owner.c
>> @@ -20,6 +20,7 @@
>>    * to use off stack temporal storage
>>    */
>>   #define PAGE_OWNER_STACK_DEPTH (16)
>> +#define PAGE_OWNER_COMM_LEN	16
> Not sure I understand why not simply use TASK_COMM_LEN ?

Yes, you are right. I thought TASK_COMM_LEN is larger than 16 without 
actually checking it. Will fix that.

Cheers,
Longman