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Date: Mon, 19 Sep 2016 21:32:38 +0200
From: Michal Hocko <mhocko@kernel.org>
To: Robert Foss <robert.foss@collabora.com>
Cc: Sonny Rao <sonnyrao@chromium.org>, Jonathan Corbet <corbet@lwn.net>,
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Subject: Re: [PATCH v5 0/3] mm, proc: Implement /proc/<pid>/totmaps
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On Mon 19-09-16 11:16:31, Robert Foss wrote:
> On 2016-09-14 05:12 AM, Michal Hocko wrote:
> > On Tue 13-09-16 13:27:39, Sonny Rao wrote:
[...]
> > > 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.

-- 
Michal Hocko
SUSE Labs