Re: [patch 14/23] hugetlb: introduce huge_pud

[Hugh Dickins <hugh@veritas.com>]

On Mon, 26 May 2008, npiggin@suse.de wrote:
> Straight forward extensions for huge pages located in the PUD
> instead of PMDs.
> 
> Signed-off-by: Andi Kleen <ak@suse.de>
> Signed-off-by: Nick Piggin <npiggin@suse.de>

Sorry, I've not looked through all these, but the subject of this one
(which should say "pud_huge" rather than "huge_pud") led me to check:
please take a look at commit aeed5fce37196e09b4dac3a1c00d8b7122e040ce,
I believe your follow_page will need to try pud_huge before pud_bad.

Though note in the comment to that commit, I'm dubious whether we
can ever actually hit that case, or need follow_huge_pmd (or your
follow_huge_pud) at all: please cross check, you might prefer to
delete the huge pmd code there rather than add huge pud code,
if you agree that there's actually no way we need it.

Hugh

> --- linux-2.6.orig/mm/memory.c
> +++ linux-2.6/mm/memory.c
> @@ -998,7 +998,13 @@ struct page *follow_page(struct vm_area_
>  	pud = pud_offset(pgd, address);
>  	if (pud_none(*pud) || unlikely(pud_bad(*pud)))
>  		goto no_page_table;
> -	
> +
> +	if (pud_huge(*pud)) {
> +		BUG_ON(flags & FOLL_GET);
> +		page = follow_huge_pud(mm, address, pud, flags & FOLL_WRITE);
> +		goto out;
> +	}
> +
>  	pmd = pmd_offset(pud, address);
>  	if (pmd_none(*pmd))
>  		goto no_page_table;

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