[PATCH] mm: hugepage accounting fix

2.6.15's hugepage faulting introduced huge_pages_needed accounting into
hugetlbfs: to count how many pages are already in cache, for spot check on
how far a new mapping may be allowed to extend the file.  But it's muddled:
each hugepage found covers HPAGE_SIZE, not PAGE_SIZE.  Once pages were
already in cache, it would overshoot, wrap its hugepages count backwards,
and so fail a harmless repeat mapping with -ENOMEM.  Fixes the problem
found by Don Dupuis.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Acked-By: Adam Litke <agl@us.ibm.com>
Acked-by: William Irwin <wli@holomorphy.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/hugetlbfs/inode.c

@@ -72,8 +72,8 @@ huge_pages_needed(struct address_space *mapping, struct vm_area_struct *vma)
 	unsigned long start = vma->vm_start;
 	unsigned long end = vma->vm_end;
 	unsigned long hugepages = (end - start) >> HPAGE_SHIFT;
-	pgoff_t next = vma->vm_pgoff;
-	pgoff_t endpg = next + ((end - start) >> PAGE_SHIFT);
+	pgoff_t next = vma->vm_pgoff >> (HPAGE_SHIFT - PAGE_SHIFT);
+	pgoff_t endpg = next + hugepages;
 
 	pagevec_init(&pvec, 0);
 	while (next < endpg) {