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SubjectRe: [PATCH RFC v2] Add /proc/pid/smaps_rollup
On Thu, 24 Aug 2017 10:55:53 +0200 Michal Hocko <> wrote:

> > If we assume that the number of VMAs is going to increase over time,
> > then doing anything we can do to reduce the overhead of each VMA
> > during PSS collection seems like the right way to go, and that means
> > outputting an aggregate statistic (to avoid whatever overhead there is
> > per line in writing smaps and in reading each line from userspace).
> >
> > Also, Dan sent me some numbers from his benchmark measuring PSS on
> > system_server (the big Android process) using smaps vs smaps_rollup:
> >
> > using smaps:
> > iterations:1000 pid:1163 pss:220023808
> > 0m29.46s real 0m08.28s user 0m20.98s system
> >
> > using smaps_rollup:
> > iterations:1000 pid:1163 pss:220702720
> > 0m04.39s real 0m00.03s user 0m04.31s system
> I would assume we would do all we can to reduce this kernel->user
> overhead first before considering a new user visible file. I haven't
> seen any attempts except from the low hanging fruid I have tried.

It's hard to believe that we'll get anything like a 5x speedup via
optimization of the existing code?

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