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Date: Mon, 12 Sep 2016 14:02:48 +0200
From: Michal Hocko <mhocko@kernel.org>
To: robert.foss@collabora.com
Cc: corbet@lwn.net, akpm@linux-foundation.org, vbabka@suse.cz,
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Subject: Re: [PATCH v5 0/3] mm, proc: Implement /proc/<pid>/totmaps
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On Mon 05-09-16 16:14:06, robert.foss@collabora.com wrote:
> From: Robert Foss <robert.foss@collabora.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.

-- 
Michal Hocko
SUSE Labs