[PATCH] hugetlb: don't allow free hugetlb count fall below reserved count

With strict page reservation, I think kernel should enforce number of free
hugetlb page don't fall below reserved count.  Currently it is possible in
the sysctl path.  Add proper check in sysctl to disallow that.
Signed-off-by: NKen Chen <kenneth.w.chen@intel.com>
Cc: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

mm/hugetlb.c

@@ -334,6 +334,7 @@ static unsigned long set_max_huge_pages(unsigned long count)
 		return nr_huge_pages;
 
 	spin_lock(&hugetlb_lock);
+	count = max(count, reserved_huge_pages);
 	try_to_free_low(count);
 	while (count < nr_huge_pages) {
 		struct page *page = dequeue_huge_page(NULL, 0);