Address space limits in IA32 linux

Address space limits in IA32 linux

[Ashok Raj]

Hello

what is the maximum addressible virtual address in a IA32 Linux system (4G?)

typically since Database requires a larger address space, does linux kernel
has any config to limit this space for kernel, so that the user process has
more address to play with?

thanks
ashok

Re: Address space limits in IA32 linux

[Rik van Riel]

On Tue, 14 May 2002, Ashok Raj wrote:

> what is the maximum addressible virtual address in a IA32 Linux system (4G?)

3 GB.

> typically since Database requires a larger address space, does linux
> kernel has any config to limit this space for kernel, so that the user
> process has more address to play with?

The kernel cannot transparently work around the limitations of the
hardware, but the database itself can create shared memory segments
which it maps and unmaps as needed.

Rik
-- 
Bravely reimplemented by the knights who say "NIH".

http://www.surriel.com/		http://distro.conectiva.com/

Re: Address space limits in IA32 linux

[Bill Davidsen]

On Wed, 15 May 2002, Jesse Pollard wrote:

> IA32 is by definition limited to 4G. Just because the Kernel may, under
> extreem duress, access more by memory management shenanigans access more,
> user processes are ALWAYS limited to a 32 bit virtual address. Even this
> is more restricted, since shared libraries and other access limits it even
> more. Usually you can stretch it to 3G, but not over that.

Actually you can go to 3.5G now, using readily available patches. However,
your unstated premise is correct, the limit using current kernel and gcc
capabilities is <4G. 

> 
> search the archives - the details are available.

Right, so is 3.5G, but I doubt that anyone with a problem not working in
3G is going to find solace in 3.5G.

-- 
bill davidsen <davidsen@tmr.com>
  CTO, TMR Associates, Inc
Doing interesting things with little computers since 1979.

Re: Address space limits in IA32 linux

[Jesse Pollard]

"Ashok Raj" <ashokr2@attbi.com>:
> 
> Hello
> 
> what is the maximum addressible virtual address in a IA32 Linux system (4G?)
> 
> typically since Database requires a larger address space, does linux kernel
> has any config to limit this space for kernel, so that the user process has
> more address to play with?
> 
> thanks
> ashok

Of course - use IA64, Sparc, or PPC.

IA32 is by definition limited to 4G. Just because the Kernel may, under
extreem duress, access more by memory management shenanigans access more,
user processes are ALWAYS limited to a 32 bit virtual address. Even this
is more restricted, since shared libraries and other access limits it even
more. Usually you can stretch it to 3G, but not over that.

search the archives - the details are available.

-------------------------------------------------------------------------
Jesse I Pollard, II
Email: pollard@navo.hpc.mil

Any opinions expressed are solely my own.