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SubjectRe: [PATCH] mm/page_owner: Record timestamp and pid
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On 11/27/20 8:23 PM, Souptick Joarder wrote:
> On Sat, Nov 28, 2020 at 12:36 AM Vlastimil Babka <vbabka@suse.cz> wrote:
>>
>> 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 :)
>
> Just a thought ... putting it inside CONFIG_PAGE_OWNER_DEBUG might be
> better if it is used
> purely for debugging purposes.

I don't think we need to introduce new config just yet, until someone makes the
case for it. Even then, it could be instead doable as an extension to
"page_owner=on" boot option.
I mean let's add those fields, but improve the changelog.

>>
>> 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 */
>> >> };
>> >>
>> >
>>
>>
>

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