Bug in VirtualAlloc
david at l8s.co.uk
Mon Aug 19 07:07:32 CDT 2002
> #define ADDRESS_SPACE_LIMIT ((void *)0xc0000000) /* top of the user address
> space */
> when making an anonymous mmap Solaris returns
> 11: ptr = (void *) 0xdf620000
> Q. Why is there a hard limit on this ? Is this a Windows thing or a Linux
It is actually a hardware feature, IIRC it is the address above which the
cache ignores process contexts (cache colours). This means that kernel
code/data is shared (in the cache) by all processes.
For the sparc reference mmu (used by all sun sparc systems for many
many years) the address is 0xe0000000. As someone put it 'the kernel
has to shoehorn itself into only 512Mb' .
I suspect you want to make ADDRESS_SPACE_LIMIT architecture dependant.
For non-x86 you can (presumably) use OS assigned mmap addresses
throughout - or is the used of known mmap addresses pervasive?
(This first became a problem as memory sizes approached 512Mb and it
no longer became possible to have all of physically memory mapped
into kernel address space).
David Laight: david at l8s.co.uk
More information about the wine-devel