Hugepage bugfix

Andrew, please apply:

Currently the hugepage code stores the hugepage destructor in the mapping field of the second of the compound pages. However, this field is never cleared again, which causes tracebacks from free_pages_check() if the hugepage is later destroyed by reducing the number in /proc/sys/vm/nr_hugepages. This patch fixes the bug by clearing the mapping field when the hugepage is freed.

Index: working-2.6/mm/hugetlb.c
===================================================================
@@ -57,6 +57,7 @@
 	BUG_ON(page_count(page));
 
 	INIT_LIST_HEAD(&page->lru);
+	page[1].mapping = NULL;
 
 	spin_lock(&hugetlb_lock);
 	enqueue_huge_page(page);

David Gibson			| For every complex problem there is a
david AT gibson.dropbear.id.au	| solution which is simple, neat and
				| wrong.
http://www.ozlabs.org/people/dgibson

Good catch; thanks.

-- wli