Messages in this thread |  | | | From | (Matthias Urlichs) | | Subject | Re: > 1GB physical on x86: Summary so far | | Date | 3 Jul 1997 21:41:44 +0200 |
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"Larry M. Augustin" <lma@varesearch.com> writes: > > However, Ingo Molvar suggests > that 4GB physical should be possible with a minor change to > PAGE_OFFSET. I don't understand this. Is he suggesting that a > 2GB/2GB user/kernel address space split as a possible solution, thus > decreasing the user space virtual memory and providing more address > space for the kernel to map physical pages? > You can't have 4 GB of kernel memory because the kernel relies on being able to map the virtual address space of the current process into kernel space too.
The memory map is rather simple: Below PAGE_OFFSET => virtual address space of user process. Above PAGE_OFFSET => real memory. The kernel also needs some space above its real memory space for vmalloc(), I/O remapping, and possibly some others I've conveniently forgotten. ;-)
A 2 GB/2 GB split should be possible. You'd probably have to do some work on the code used to set up the page tables, though -- I didn't check.
On the other hand, I'd be surprised to see a mainboard that supports even 1 GByte of memory reliably... most max out at 512 these days, and their performance sucks above the 64-MB threshold if you rely on your vendor's claim that the tag RAM they installed is actually big enough. :-(
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