[RFC] process /proc/PID/smaps vs /proc/PID/smaps_rollup

[Sergey Senozhatsky]

Hello,

One of our unprivileged daemon process needs process PSS info. That
info is usually available in /proc/PID/smaps on per-vma basis, on
in /proc/PID/smaps_rollup as a bunch of accumulated per-vma values.
The latter one is much faster and simpler to get, but, unlike smaps,
smaps_rollup requires PTRACE_MODE_READ, which we don't want to
grant to our unprivileged daemon.

So the question is - can we get, somehow, accumulated PSS info from
a non-privileged process? (Iterating through all process' smaps
vma-s consumes quite a bit of CPU time). This is related to another
question - why do smaps and smaps_rollup have different permission
requirements?

	-ss