hugetlb: chg cannot become less than 0

chg is unsigned, so it cannot be less than 0.

Also, since region_chg returns long, let vma_needs_reservation() forward
this to alloc_huge_page().  Store it as long as well.  all callers cast it
to long anyway.

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Cc: Andy Whitcroft <apw@shadowen.org>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Adam Litke <agl@us.ibm.com>
Cc: Johannes Weiner <hannes@saeurebad.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/hugetlb.c

@@ -918,7 +918,7 @@ static void return_unused_surplus_pages(struct hstate *h,
  * an instantiated the change should be committed via vma_commit_reservation.
  * No action is required on failure.
  */
-static int vma_needs_reservation(struct hstate *h,
+static long vma_needs_reservation(struct hstate *h,
 			struct vm_area_struct *vma, unsigned long addr)
 {
 	struct address_space *mapping = vma->vm_file->f_mapping;
@@ -933,7 +933,7 @@ static int vma_needs_reservation(struct hstate *h,
 		return 1;
 
 	} else  {
-		int err;
+		long err;
 		pgoff_t idx = vma_hugecache_offset(h, vma, addr);
 		struct resv_map *reservations = vma_resv_map(vma);
 
@@ -969,7 +969,7 @@ static struct page *alloc_huge_page(struct vm_area_struct *vma,
 	struct page *page;
 	struct address_space *mapping = vma->vm_file->f_mapping;
 	struct inode *inode = mapping->host;
-	unsigned int chg;
+	long chg;
 
 	/*
 	 * Processes that did not create the mapping will have no reserves and