[PATCH] mm: hugetlb: fix pgoff computation when unmapping page from vma

[Hillf Danton]

The computation for pgoff is incorrect, at least with

	(vma->vm_pgoff >> PAGE_SHIFT)

involved. It is fixed with the available method if HPAGE_SIZE is concerned in
page cache lookup.

Cc: Michal Hocko <mhocko@xxxxxxx>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Hillf Danton <dhillf@xxxxxxxxx>
---

--- a/mm/hugetlb.c	Tue Dec 20 21:26:30 2011
+++ b/mm/hugetlb.c	Tue Dec 20 21:40:44 2011
@@ -2315,8 +2315,7 @@ static int unmap_ref_private(struct mm_s
 	 * from page cache lookup which is in HPAGE_SIZE units.
 	 */
 	address = address & huge_page_mask(h);
-	pgoff = ((address - vma->vm_start) >> PAGE_SHIFT)
-		+ (vma->vm_pgoff >> PAGE_SHIFT);
+	pgoff = linear_hugepage_index(vma, address);
 	mapping = (struct address_space *)page_private(page);

 	/*
--
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