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Subject: Re: [PATCH] mm/page_owner: Record timestamp and pid
To:     Georgi Djakov <georgi.djakov@linaro.org>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        sudaraja@codeaurora.org, pratikp@codeaurora.org,
        lmark@codeaurora.org
References: <20201112184106.733-1-georgi.djakov@linaro.org>
 <20201112111436.c5deeadd3578877fc0b844a1@linux-foundation.org>
 <02f682e2-0e9b-76a8-04fa-487891e18bdf@suse.cz>
 <3ef3d770-d74b-5588-6672-f092c1526461@linaro.org>
From:   Vlastimil Babka <vbabka@suse.cz>
Message-ID: <bdf8727f-1191-34bd-d8ec-69b2a3d50c1b@suse.cz>
Date:   Fri, 27 Nov 2020 20:06:38 +0100
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On 11/27/20 7:57 PM, Georgi Djakov wrote:
> Hi Vlastimil,
> 
> Thanks for the comment!
> 
> On 11/27/20 19:52, Vlastimil Babka wrote:
>> On 11/12/20 8:14 PM, Andrew Morton wrote:
>>> On Thu, 12 Nov 2020 20:41:06 +0200 Georgi Djakov <georgi.djakov@linaro.org> 
>>> wrote:
>>>
>>>> From: Liam Mark <lmark@codeaurora.org>
>>>>
>>>> Collect the time for each allocation recorded in page owner so that
>>>> allocation "surges" can be measured.
>>>>
>>>> Record the pid for each allocation recorded in page owner so that
>>>> the source of allocation "surges" can be better identified.
>>>
>>> Please provide a description of why this is considered useful.  What
>>> has it been used for, what problems has it been used to solve?
>> 
>> Worth noting that on x86_64 it doubles the size of struct page_owner
>> from 16 bytes to 32, so it better be justified:
> 
> Well, that's true. But for debug options there is almost always some penalty.
> The timestamp and pid information is very useful for me (and others, i believe)
> when doing memory analysis. On a crash for example, we can get this information
> from kdump (or RAM-dump) and look into it to catch memory allocation problems
> more easily.

Right. Btw, you should add printing the info to __dump_page_owner().

> If you find the above argument not strong enough, how about a separate config
> option for this? Maybe something like CONFIG_PAGE_OWNER_EXTENDED, which could
> be enabled in addition to CONFIG_PAGE_OWNER?

It might be strong enough if it's mentioned in changelog, and also what exactly 
the space tradeoff is :)

You can also mention that SLUB object tracking has also pid+timestamp.

> Thanks,
> Georgi
> 
>> 
>> struct page_owner {
>>          short unsigned int         order;                /*     0     2 */
>>          short int                  last_migrate_reason;  /*     2     2 */
>>          gfp_t                      gfp_mask;             /*     4     4 */
>>          depot_stack_handle_t       handle;               /*     8     4 */
>>          depot_stack_handle_t       free_handle;          /*    12     4 */
>>          u64                        ts_nsec;              /*    16     8 */
>>          int                        pid;                  /*    24     4 */
>> 
>>          /* size: 32, cachelines: 1, members: 7 */
>>          /* padding: 4 */
>>          /* last cacheline: 32 bytes */
>> };
>> 
>