Messages in this thread | | | Date | Thu, 3 Jul 1997 08:25:48 -0400 (EDT) | From | "Richard B. Johnson" <> | Subject | Re: > 1GB RAM on x86 ? |
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On Wed, 2 Jul 1997, David S. Miller wrote:
> Date: Wed, 2 Jul 1997 16:58:40 -0700 > From: "Larry M. Augustin" <lma@varesearch.com> > > Is there a 1GB physical limit, what's the reason for the limit, and > what would need to change to increase this to 4GB? (i.e. Where did > those other 2 bits go?) > > Talk to Linus. > > I also seem to be seeing a limit on swap space of 1GB. What about > increasing that too? > > Talk to Linus. >
The __comment__ in /usr/src/linux/arch/i386/kernel/head.S was not updated when the address space was updated. Everybody has 4GB of virtual address space. It is not, as you say, 2 bits. Every virtual page requires a static GDT, and a PTE if it is ever accessed.
Note that providing more GDTs than can ever be used wastes real RAM.
From head.S ..........
/* * This gdt setup gives the kernel a 1GB address space at virtual * address 0xC0000000 - space enough for expansion, I hope. * * This contains up to 8192 quadwords depending on NR_TASKS - 64kB of * gdt entries. Ugh. * * NOTE! Make sure the gdt descriptor in head.S matches this if you * change anything. */ ENTRY(gdt) .quad 0x0000000000000000 /* NULL descriptor */ .quad 0x0000000000000000 /* not used */ .quad 0x00cf9a000000ffff /* 0x10 kernel 4GB code at 0x00000000 */ .quad 0x00cf92000000ffff /* 0x18 kernel 4GB data at 0x00000000 */ .quad 0x00cffa000000ffff /* 0x23 user 4GB code at 0x00000000 */ .quad 0x00cff2000000ffff /* 0x2b user 4GB data at 0x00000000 */ .quad 0x0000000000000000 /* not used */ .quad 0x0000000000000000 /* not used */ .fill 2*NR_TASKS,8,0 /* space for LDT's and TSS's etc */ #ifdef CONFIG_APM .quad 0x00c09a0000000000 /* APM CS code */
Cheers, DJ -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Richard B. Johnson Analogic Corporation Email : rjohnson@analogic.com, johnson@analogic.com Penguin : Linux version 2.1.44 on an i586 machine (66.15 BogoMips). Warning : It's hard to stay on the trailing edge of technology. -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
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