-XX:+MaximizeHeapSize?

[Y Srinivas Ramakrishna]

Is there dependable public documentation on the semantics of
various memory overcommit modes in Linux and especially the
one you have in mind here?

Pointers, anyone?

-- ramki.

----- Original Message -----
From: Florian Weimer <fw at deneb.enyo.de>
Date: Wednesday, July 11, 2007 12:33 pm
Subject: Re: -XX:+MaximizeHeapSize?
To: Jon Masamitsu <Jon.Masamitsu at Sun.COM>
Cc: hotspot-gc-dev at openjdk.java.net


> * Jon Masamitsu:
> 
> > Yes, hotspot does do a reserve of a continuous address space for the
> > entire heap at initialization with an mmap call using
> >
> >    MAP_PRIVATE | MAP_NORESERVE | MAP_ANONYMOUS
> >
> > As the heap is actually expanded the space is mmap'ed with
> >
> >    MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS
> >
> > so it can actually be used.  See the reserve_memory() and
> > commit_memory() methods
> > in os/linux/vm/os_linux.cpp for the details.
> 
> This is not sufficient in vm.overcommit_memory = 2 mode.  Without
> PROT_NONE, the allocation still counts against the beancounter limit.
> Perhaps this is a kernel bug, but is has been this way for quite some
> time.