[PATCH 21/35] Do not check for compound pages during the page allocator sanity checks

[Mel Gorman]

A number of sanity checks are made on each page allocation and free
including that the page count is zero. page_count() checks for
compound pages and checks the count of the head page if true. However,
in these paths, we do not care if the page is compound or not as the
count of each tail page should also be zero.

This patch makes two changes to the use of page_count() in the free path. It
converts one check of page_count() to a VM_BUG_ON() as the count should
have been unconditionally checked earlier in the free path. It also avoids
checking for compound pages.

[mel@xxxxxxxxx: Wrote changelog]
Signed-off-by: Nick Piggin <nickpiggin@xxxxxxxxxxxx>
---
 mm/page_alloc.c |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d297780..2704092 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -425,7 +425,7 @@ static inline int page_is_buddy(struct page *page, struct page *buddy,
 		return 0;
 
 	if (PageBuddy(buddy) && page_order(buddy) == order) {
-		BUG_ON(page_count(buddy) != 0);
+		VM_BUG_ON(page_count(buddy) != 0);
 		return 1;
 	}
 	return 0;
@@ -501,7 +501,7 @@ static inline int free_pages_check(struct page *page)
 {
 	if (unlikely(page_mapcount(page) |
 		(page->mapping != NULL)  |
-		(page_count(page) != 0)  |
+		(atomic_read(&page->_count) != 0) |
 		(page->flags & PAGE_FLAGS_CHECK_AT_FREE))) {
 		bad_page(page);
 		return 1;
@@ -646,7 +646,7 @@ static int prep_new_page(struct page *page, int order, gfp_t gfp_flags)
 {
 	if (unlikely(page_mapcount(page) |
 		(page->mapping != NULL)  |
-		(page_count(page) != 0)  |
+		(atomic_read(&page->_count) != 0)  |
 		(page->flags & PAGE_FLAGS_CHECK_AT_PREP))) {
 		bad_page(page);
 		return 1;
-- 
1.5.6.5

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