Review request for 5049299

[Andrew Haley]

Martin Buchholz wrote:
> I did a little research.
> 
> The overcommitment policy on Linux is configurable
> http://lxr.linux.no/linux/Documentation/vm/overcommit-accounting
> Of course, almost everyone will use the default "heuristic" policy,
> and in this case the COW memory after fork() is subject to overcommit
> accounting, which *may* cause the fork to fail.

Sure, it *may*, but I don't think it's at all common.

> http://lkml.indiana.edu/hypermail/linux/kernel/0902.1/01777.html
> If a solution using clone(CLONE_VM ...) can be made to work,
> subprocess creation will be a little cheaper and significantly more
> reliable.

Maybe, but I think that needs to be measured before any changes are made.
I'm not opposed to such a change that makes a real improvement, but I'm
not convinced it will.  As usual, I'm happy to be proved wrong.

There may be a kernel bug in the case described in the mail above: it
certainly should be possible to fork a 38 GB process on a system with
64 GB RAM.  If so, I expect that this will be fixed long before any Java
VM change makes it into production.

Andrew.