[Sidefx-houdini-list] render-memory problem

Chris AtLee catlee at sidefx.com
Tue Aug 8 12:52:16 EDT 2006

Sort of ;-)

On a 32 bit machine, the address space is 4 GB large, but not all of
that is usable by the application, part of the address space is reserved
for use by the kernel. Older linux kernels reserved 2GB for the kernel
leaving 2GB for the application. More recent kernels reserve only 1GB,
leaving 3GB for the application. So this means that the size of the
application + libraries + allocated memory can never exceed 3 GB on a
32bit linux box. On windows the limit is a bit lower, somewhere around 2
GB I think.

As for swapping, if you have a system with 4 GB of RAM and 2 GB of swap,
you will start swapping once the amount of memory used by your
applications exceeds 4 GB. This can't happen in a single application
(since the limit is between 2 and 3 GB per application), but it's pretty
easy to hit with multiple memory hungry applications.

Mark A. Bolstad wrote:
> Sort of ;-)
> <Begin dredging memory for old OS stuff; Proceed with caution>
> The maximum addressable space in 32 bits is 4 GB. So, the most a single
> application can allocate is 4 GB. However, the OS has a few additional
> tricks up it's sleeve, such that it can address a larger space through
> the virtual memory management (VMM) system. So in theory, you could have
> two 3GB processes running simultaneously, one in RAM, and one swapped
> out, or both partially swapped out. And the reason this works is that
> most VMM systems use a paging system through the file system (which uses
> 64-bit pointers), so you only need to keep track of the pages swapped in
> and out, and not the physical addresses (although you do need to map
> pages to memory addresses and to the file system, but that's another
> lecture).
> </Begin dredging memory for old OS stuff; Proceed with caution>
> Mark
> P. Alex Lim wrote:
>> Hi Mark,
>> Just out of curiosity, if you have 4GB of RAM and 2GB of swap memory,
>> and once you hit that 4GB RAM limit, does the system still goes into
>> swap or is the 4GB "it"?
>> I wasn't too sure if this limit applies to RAM usage only or if it's the
>> 32bits OS in general.
>> Thanks,
>> Alex

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