Re: [PATCH v5 0/3] mm, proc: Implement /proc/<pid>/totmaps

On Mon, Sep 19, 2016 at 5:27 PM, Robert Foss [off-list ref] wrote:

On 2016-09-19 03:32 PM, Michal Hocko wrote:

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On Mon 19-09-16 11:16:31, Robert Foss wrote:

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On 2016-09-14 05:12 AM, Michal Hocko wrote:

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On Tue 13-09-16 13:27:39, Sonny Rao wrote:

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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?

yes basically return the same value if called within HZ or something
similar. But that assumes that statm latency really matters and it is
called often enough.

Any single application querying more often than HZ, would presumably do so
for accuracy reasons.
However for multiple applications that combined query more often than HZ,
this would most definitely be halpful in terms of performance.

@Sonny, does chromiumos fall into the first or second category?

It's a single application -- and it definitely doesn't query at HZ --
especially given how long it takes to gather the data :-)