Re: [rfc] dynamic 3-level / 4-level page table

Robin Holt
2006-04-28T15:33:37Z

On Thu, Apr 27, 2006 at 07:09:17PM -0700, Chen, Kenneth W wrote:
> --- ./arch/ia64/kernel/ivt.S.orig 2006-04-27 19:21:55.000000000 -0700
> +++ ./arch/ia64/kernel/ivt.S 2006-04-27 19:46:44.000000000 -0700
> @@ -142,16 +142,16 @@ ENTRY(vhpt_miss)
> (p7) dep r17=r18,r17,3,(PAGE_SHIFT-6) // r17=pgd_offset for region[0-4]
> cmp.eq p7,p6=0,r21 // unused address bits all zeroes?
> #ifdef CONFIG_PGTABLE_4
> - shr.u r28=r22,PUD_SHIFT // shift pud index into position
> + extr.u r28=r22,PUD_SHIFT,11 // get pud index

How well does this work with different page sizes?

> +
> +#ifdef CONFIG_PGTABLE_4
> +int pgtbl3;
> +static __init int setup_pgtbl3(char *s)
> +{
> + pgtbl3 = 1;
> + return 0;
> +}
> +early_param("pgtbl3", setup_pgtbl3);
> +#endif

What about taking out CONFIG_PGTABLE_*, having the default be 3, and have the
boot option enable 4 levels? I haven't given this much though yet, but my
first reaction was that would be the correct way to go.

Thanks,
Robin