hugetlb: pull gigantic page initialisation out of the default path

As we can determine exactly when a gigantic page is in use we can optimise
the common regular page cases by pulling out gigantic page initialisation
into its own function.  As gigantic pages are never released to buddy we
do not need a destructor.  This effectivly reverts the previous change to
the main buddy allocator.  It also adds a paranoid check to ensure we
never release gigantic pages from hugetlbfs to the main buddy.

Signed-off-by: Andy Whitcroft <apw@shadowen.org>
Cc: Jon Tollefson <kniht@linux.vnet.ibm.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: <stable@kernel.org>		[2.6.27.x]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 21 insertions, 7 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d0a240fbb8bf..54069e64e3a8 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -263,24 +263,39 @@ void prep_compound_page(struct page *page, unsigned long order)
 {
 	int i;
 	int nr_pages = 1 << order;
+
+	set_compound_page_dtor(page, free_compound_page);
+	set_compound_order(page, order);
+	__SetPageHead(page);
+	for (i = 1; i < nr_pages; i++) {
+		struct page *p = page + i;
+
+		__SetPageTail(p);
+		p->first_page = page;
+	}
+}
+
+#ifdef CONFIG_HUGETLBFS
+void prep_compound_gigantic_page(struct page *page, unsigned long order)
+{
+	int i;
+	int nr_pages = 1 << order;
 	struct page *p = page + 1;
 
 	set_compound_page_dtor(page, free_compound_page);
 	set_compound_order(page, order);
 	__SetPageHead(page);
-	for (i = 1; i < nr_pages; i++, p++) {
-		if (unlikely((i & (MAX_ORDER_NR_PAGES - 1)) == 0))
-			p = pfn_to_page(page_to_pfn(page) + i);
+	for (i = 1; i < nr_pages; i++, p = mem_map_next(p, page, i)) {
 		__SetPageTail(p);
 		p->first_page = page;
 	}
 }
+#endif
 
 static void destroy_compound_page(struct page *page, unsigned long order)
 {
 	int i;
 	int nr_pages = 1 << order;
-	struct page *p = page + 1;
 
 	if (unlikely(compound_order(page) != order))
 		bad_page(page);
@@ -288,9 +303,8 @@ static void destroy_compound_page(struct page *page, unsigned long order)
 	if (unlikely(!PageHead(page)))
 			bad_page(page);
 	__ClearPageHead(page);
-	for (i = 1; i < nr_pages; i++, p++) {
-		if (unlikely((i & (MAX_ORDER_NR_PAGES - 1)) == 0))
-			p = pfn_to_page(page_to_pfn(page) + i);
+	for (i = 1; i < nr_pages; i++) {
+		struct page *p = page + i;
 
 		if (unlikely(!PageTail(p) |
 				(p->first_page != page)))