[OSM-dev] mmap() (was: Re: Some statistics for file-format -development)

[Sascha Silbe]

On Tue, Nov 25, 2008 at 08:47:16AM +0100, Marcus Wolschon wrote:

> Okay, on a big AMD-multicore-laptop the limit in Java seems to be
> 1GB of memory-mapped files.
That's pretty small given that kernel/user split is usually 2G/2G or 
even 3G/1G...

> Ulimit was "unlimited" and --XX:MaxDirectMemorySize was set to 32GB
> -Xmx was a few GB. I am using the current Java6 -patchlevel 10 from
> Sun.
Have you tried using a smaller -Xmx size? I have the impression that 
Java allocates the maximum allowed size directly on startup, relying on 
the OS to do lazy allocation of pages. If that's the case, reducing -Xmx 
should increase free virtual address space, allowing bigger memory 
mappings.

> I'd like to try this on a 64bit-Linux on that box but don't know how 
> to
> do that yet. Any help on turning a debian 32bit into a 64-bit or 
> running
> a 64bit-VM in a 32bit-Linux?
I don't think that's possible. Both 32bit and 64bit userspace and 
emulation work with a 64bit kernel, but at least 64bit userspace on a 
32bit kernel isn't possible.

CU Sascha

-- 
http://sascha.silbe.org/
http://www.infra-silbe.de/
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