On Sat, 21 Sep 2002, Andrew Morton wrote:

Hugh Dickins wrote:

quoted

On Sat, 21 Sep 2002, Andrew Morton wrote:

quoted

running 10,000 tiobench threads I'm showing 23 gigs of
`Commited_AS'.  Is this right?  Those pages are shared,
and if they're not PROT_WRITEable then there's no way in
which they can become unshared?   Seems to be excessively
pessimistic?

quoted

Committed_AS certainly errs on the pessimistic side, that's
what it's about.  How much swap do you have i.e. is 23GB
committed impossible, or just surprising to you?  Does the
number go back to what it started off from when you kill
off the tests?  How are "those pages" allocated e.g. what
mmap args?

I have 7G physical, 4G swap.

When I wondered if impossible, of course I was overlooking
that you wouldn't be running with strict commit limitation,
so "impossible" is quite difficult to reach.

"those pages" were just used by some scruffy perl script 
running `./tiotest &' ten thousand times.  I assume it's
shared executable text.

When I run tiotest here, /proc/<pid>/maps shows a little over
2MB of rwxp or rw-p areas, all to be counted in Committed_AS.
So 23GB for 10,000 of them sounds reasonable.  You think you
have less PROT_WRITE or less MAP_PRIVATE than I'm seeing?

It seems very unlikely (impossible?) that those pages will
ever become unshared.

I expect it's very unlikely (short of application bugs) that
those pages would become unshared; but they have been mapped
in such a way that the process is entitled to unshare them,
therefore they have been counted.  A good example of why
Linux does not impose strict commit accounting, and why
you may choose not to use Alan's strict accounting policy.

Hugh

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/