[PATCH 01/22] mm, page_alloc: Only check PageCompound for high-order pages

[Mel Gorman <mgorman@techsingularity.net>]

order-0 pages by definition cannot be compound so avoid the check in the
fast path for those pages.

Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
---
 mm/page_alloc.c | 25 +++++++++++++++++--------
 1 file changed, 17 insertions(+), 8 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 59de90d5d3a3..5d205bcfe10d 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1024,24 +1024,33 @@ void __meminit reserve_bootmem_region(unsigned long start, unsigned long end)
 
 static bool free_pages_prepare(struct page *page, unsigned int order)
 {
-	bool compound = PageCompound(page);
-	int i, bad = 0;
+	int bad = 0;
 
 	VM_BUG_ON_PAGE(PageTail(page), page);
-	VM_BUG_ON_PAGE(compound && compound_order(page) != order, page);
 
 	trace_mm_page_free(page, order);
 	kmemcheck_free_shadow(page, order);
 	kasan_free_pages(page, order);
 
+	/*
+	 * Check tail pages before head page information is cleared to
+	 * avoid checking PageCompound for order-0 pages.
+	 */
+	if (order) {
+		bool compound = PageCompound(page);
+		int i;
+
+		VM_BUG_ON_PAGE(compound && compound_order(page) != order, page);
+
+		for (i = 1; i < (1 << order); i++) {
+			if (compound)
+				bad += free_tail_pages_check(page, page + i);
+			bad += free_pages_check(page + i);
+		}
+	}
 	if (PageAnon(page))
 		page->mapping = NULL;
 	bad += free_pages_check(page);
-	for (i = 1; i < (1 << order); i++) {
-		if (compound)
-			bad += free_tail_pages_check(page, page + i);
-		bad += free_pages_check(page + i);
-	}
 	if (bad)
 		return false;
 
-- 
2.6.4

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