# Re: \[PATCH RFC v2\] Add /proc/pid/smaps\_rollup

- From: Andrew Morton \<hidden\>
- Date: 2017-08-25 21:16:37 
- List: linux-api
- Page: https://ratatoskr.run/linux-api/2017/08/124970
- Thread: https://ratatoskr.run/linux-fsdevel/2017/08/124976/t.md

```text
On Thu, 24 Aug 2017 10:55:53 +0200 Michal Hocko [ref] 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?
```