linux-kernel - Re: [PATCH RFC v2] Add /proc/pid/smaps

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Message-Id: <20170825141637.f11a36a9997b4b705d5b6481@linux-foundation.org>
Date:   Fri, 25 Aug 2017 14:16:37 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Tim Murray <timmurray@...gle.com>,
        Sonny Rao <sonnyrao@...omium.org>,
        Daniel Colascione <dancol@...gle.com>,
        Minchan Kim <minchan@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Joel Fernandes <joelaf@...gle.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, Linux-MM <linux-mm@...ck.org>,
        Robert Foss <robert.foss@...labora.com>,
        linux-api@...r.kernel.org, Luigi Semenzato <semenzato@...gle.com>
Subject: Re: [PATCH RFC v2] Add /proc/pid/smaps_rollup

On Thu, 24 Aug 2017 10:55:53 +0200 Michal Hocko <mhocko@...nel.org> 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?