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

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Date:   Mon, 12 Sep 2016 08:31:36 -0700
From:   Sonny Rao <sonnyrao@...omium.org>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Robert Foss <robert.foss@...labora.com>,
        Jonathan Corbet <corbet@....net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Hugh Dickins <hughd@...gle.com>,
        Konstantin Khlebnikov <koct9i@...il.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        John Stultz <john.stultz@...aro.org>,
        Minchan Kim <minchan@...nel.org>, ross.zwisler@...ux.intel.com,
        jmarchan@...hat.com, Johannes Weiner <hannes@...xchg.org>,
        Kees Cook <keescook@...omium.org>, oleg@...hat.com,
        Al Viro <viro@...iv.linux.org.uk>,
        Mateusz Guzik <mguzik@...hat.com>,
        Janis Danisevskis <jdanis@...gle.com>, calvinowens@...com,
        Alexey Dobriyan <adobriyan@...il.com>, ebiederm@...ssion.com,
        seth.forshee@...onical.com, tixxdz@...il.com,
        linux-doc@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Ben Zhang <benzh@...omium.org>,
        Bryan Freed <bfreed@...omium.org>,
        Filipe Brandenburger <filbranden@...omium.org>,
        Jann Horn <jann@...jh.net>, linux-api@...r.kernel.org,
        Jacek Anaszewski <j.anaszewski@...sung.com>
Subject: Re: [PATCH v5 0/3] mm, proc: Implement /proc/<pid>/totmaps

On Mon, Sep 12, 2016 at 5:02 AM, Michal Hocko <mhocko@...nel.org> wrote:
> On Mon 05-09-16 16:14:06, robert.foss@...labora.com wrote:
>> From: Robert Foss <robert.foss@...labora.com>
>>
>> This series provides the /proc/PID/totmaps feature, which
>> summarizes the information provided by /proc/PID/smaps for
>> improved performance and usability reasons.
>>
>> A use case is to speed up monitoring of memory consumption in
>> environments where RSS isn't precise.
>>
>> For example Chrome tends to many processes which have hundreds of VMAs
>> with a substantial amount of shared memory, and the error of using
>> RSS rather than PSS tends to be very large when looking at overall
>> memory consumption.  PSS isn't kept as a single number that's exported
>> like RSS, so to calculate PSS means having to parse a very large smaps
>> file.
>>
>> This process is slow and has to be repeated for many processes, and we
>> found that the just act of doing the parsing was taking up a
>> significant amount of CPU time, so this patch is an attempt to make
>> that process cheaper.
>
> I still maintain my concerns about a single pss value. It might work in
> a very specific situations where the consumer knows what is shared but
> other than that the value can be more misleading than helpful. So a NACK
> from me until I am shown that this is usable in general and still
> helpful.

I know you think Pss isn't useful in general (though I'll point out
two other independent people said they found it useful) but how about
the other fields like Swap, Private_Dirty and Private_Shared?

If we removed Pss would you still NACK it?

>
> --
> Michal Hocko
> SUSE Labs