Re: [PATCH 1/3] [FIX] hugetlb: Fix broken fs quota management

[Dave Hansen <haveblue@us.ibm.com>]

On Wed, 2007-10-24 at 06:23 -0700, Adam Litke wrote:
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -685,7 +685,17 @@ void __unmap_hugepage_range(struct vm_area_struct *vma, unsigned long start,
>  	flush_tlb_range(vma, start, end);
>  	list_for_each_entry_safe(page, tmp, &page_list, lru) {
>  		list_del(&page->lru);
> -		put_page(page);
> +		if (put_page_testzero(page)) {
> +			/*
> +			 * When releasing the last reference to a page we must
> +			 * credit the quota.  For MAP_PRIVATE pages this occurs
> +			 * when the last PTE is cleared, for MAP_SHARED pages
> +			 * this occurs when the file is truncated.
> +			 */
> +			VM_BUG_ON(PageMapping(page));
> +			hugetlb_put_quota(vma->vm_file->f_mapping);
> +			free_huge_page(page);
> +		}
>  	}
>  }

That's a pretty good mechanism to use.   

This particular nugget is for MAP_PRIVATE pages only, right?  The shared
ones should have another ref out on them for the 'mapping' too, so won't
get released at unmap, right?

It isn't obvious from the context here, but how did free_huge_page() get
called for these pages before?

Can you use free_pages_check() here to get some more comprehensive page
tests?  Just a cursory look at it makes me think that it should work.  

-- Dave

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