Increase memory limits for IcedTea
aph at redhat.com
Wed Oct 10 03:17:07 PDT 2007
Peter B. Kessler writes:
> Andrew Haley wrote:
> > Peter B. Kessler writes:
> > > Andrew Haley wrote:
> > >
> > > > Peter B. Kessler writes:
> > > > ....
> > > >
> > > > > The right solution is to make it so the heap doesn't have to
> > > > > be in contiguous memory. Anyone want to help work on that?
> > > >
> > > > Hmm. Surely it's better / more efficient to ask the kernel to map a
> > > > contiguous range of pages rather than for the VM do more work in user
> > > > space. The nice thing about Java on Linux is that we're in a position
> > > > to ask the kernel engineers to help us with what we need.
> > >
> > > You are probably thinking of reasonable users who want to run in
> > > reasonable heaps that leave plenty of address space for other bits
> > > of the process. We get the phone calls from the folks that want
> > > to shoehorn the largest possible heap into their address space.
> > > Contiguous heaps are pain for them.
> > Yes, I see. I suppose I would rather take the position today that
> > such people really should be using 64-bit systems: AFAIK it has not
> > been possible to buy a (new) 32-bit x86-based machine for a year or
> > so. So, while I accept your point, it's more of an issue for legacy
> > hardware. (I'm only considering desktop systems and servers here:
> > embedded Java is a whole 'nother ball of wax.)
> The "problem" is that all these spiffy 64-bit systems can also
> run 32-bit JVM's. Running the same app (or benchmark) on a
> 32-bit JVM and a 64-bit JVM quickly convinces you that you want
> to stay on a 32-bit JVM for as long as you can. So you milk
> that address space for all it's worth.
Ah, I see. That's really interesting, and a little surprising to me:
gcc/gcj runs faster in 64-bit mode than in 32-bit mode, so we've never
had to make such a tradeoff. I think the main reason for this is that
we can do much better register allocation on x86_64 than on x86, and
the calling conventions are much better. I hadn't realized that the
Sun JVM took such a hit.
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