linux-kernel - Re: size of swapped-out part of the process

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Message-ID: <Pine.LNX.4.64.0811171343340.11044@blonde.site>
Date:	Mon, 17 Nov 2008 14:02:59 +0000 (GMT)
From:	Hugh Dickins <hugh@...itas.com>
To:	Victoria Muntean <vikimun@...il.com>
cc:	Kernel Linux <linux-kernel@...r.kernel.org>
Subject: Re: size of swapped-out part of the process

On Mon, 17 Nov 2008, Victoria Muntean wrote:
> How can I calculate size of swapped-out part of the process from
> /proc/PID/*, even if approximately ?
> For example, I have VmSize=1216192 kB, VmRSS = 628788 kB, but global
> swap-in-use==0.
> Hence (VmSize - VmRSS) is far from being swapped-out part of the
> process. What is ?

I'm sorry, we don't record those numbers per process or per mm,
so you won't find them in /proc/PID/status or /proc/PID/statm.

And we'd probably resist accepting a patch to add them,
so as not to enlarge key data structures to hold them.

There's also an ambiguity about what "swapped-out" means: does
it include shared file pages which were once mapped into the
process, but have since been freed under memory pressure?

But it looks like you're interested in swapped-out to mean written
on swap.  In that case, if you have CONFIG_PROC_PAGE_MONITOR=y,
you can read /proc/PID/smaps and add up all the "Swap:" lines.

But don't keep reading it in a tight loop: that would
tend to detract from the performance of your system.

Hugh
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