Re: [RFC] virtual memmap for sparsemem [2/2] for ia64.

From: Christoph Lameter <clameter_at_sgi.com>
Date: 2006-10-20 11:45:18
On Fri, 20 Oct 2006, KAMEZAWA Hiroyuki wrote:

> Maximun phyisical address size of Itanium2 looks 50bits. Then, we need
> sizeof (struct page) * (50 - PAGE_SHIFT) size of virtual address space.

Right. That is 4TB which can be a portion of the 128TB VMALLOC space. Have 
you seen my patchset that does the calculation on linux-ia674?

> 
> #ifdef CONFIG_PGTABLE_4
> #define PGDIR_SHIFT             (PUD_SHIFT + (PTRS_PER_PTD_SHIFT))
> #else
> #define PGDIR_SHIFT             (PMD_SHIFT + (PTRS_PER_PTD_SHIFT))
> #endif
> 
> Then, considering PAGE_SHIFT=14 case, 
> 4-level-page-table mapsize:(1 << (4 * PAGE_SHIFT - 9) -> (1 << 47)
> 3-level-page-table mapsize:(1 << (3 * PAGE_SHIFT - 6) -> (1 << 36)

You are missing one PAGE_SHIFT (the page that is referred to !)

3 level is 47. 4 level is 58. 
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Received on Fri Oct 20 11:45:34 2006

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