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SubjectRe: [PATCH v5 0/3] mm, proc: Implement /proc/<pid>/totmaps
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On 2016-09-14 05:12 AM, Michal Hocko wrote:
> On Tue 13-09-16 13:27:39, Sonny Rao wrote:
>> On Tue, Sep 13, 2016 at 12:12 AM, Michal Hocko <mhocko@kernel.org> wrote:
>>> On Mon 12-09-16 10:28:53, Sonny Rao wrote:
>>>> On Mon, Sep 12, 2016 at 10:15 AM, Michal Hocko <mhocko@kernel.org> wrote:
>>>>> On Mon 12-09-16 08:31:36, Sonny Rao wrote:
>>> [...]
>>>>>> but how about the other fields like Swap, Private_Dirty and
>>>>>> Private_Shared?
>>>>>
>>>>> Private_Shared can be pretty confusing as well without the whole context
>>>>> as well see my other emails in the original thread (just to remind
>>>>> shmem/tmpfs makes all this really confusing).
>>>>
>>>> But this is exactly the issue -- RSS is can be just as confusing if
>>>> you don't know something about the application.
>>>
>>> I agree that rss can be confusing but we will not make the situation any
>>> better if we add yet another confusing metric.
>>>
>>>> I think the issue is
>>>> how common that situation is, and you seem to believe that it's so
>>>> uncommon that it's actually better to keep the information more
>>>> difficult to get for those of us who know something about our systems.
>>>>
>>>> That's fine, I guess we just have to disagree here, thanks for look at this.
>>>
>>> I think you should just step back and think more about what exactly
>>> you expect from the counter(s). I believe what you want is an
>>> estimate of a freeable memory when the particular process dies or is
>>> killed. That would mean resident single mapped private anonymous memory
>>> + unlinked single mapped shareable mappings + single mapped swapped out
>>> memory. Maybe I've missed something but it should be something along
>>> those lines. Definitely something that the current smaps infrastructure
>>> doesn't give you, though.
>>
>> Yes your description of what we want is pretty good. Having a
>> reasonable lower bound on the estimate is fine, though we probably
>> want to break out swapped out memory separately.
>
> Why would you want to separate that?
>
>> Given that smaps
>> doesn't provide this in a straightforward way, what do you think is
>> the right way to provide this information?
>
> I would be tempted to sneak it into /proc/<pid>/statm because that looks
> like a proper place but getting this information is not for free
> performance wise so I am not really sure something that relies on this
> file would see unexpected stalls. Maybe this could be worked around by
> some caching... I would suggest to check who is actually using this file
> (top/ps etc...)

What would this caching look like? Can any information be re-used
between vma walks?

>
> If this would be unacceptable then a new file could be considered.
>

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