> 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
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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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