[PATCH 01/24] mm, page_alloc: Only check PageCompound for high-order pages

[Mel Gorman]

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

Signed-off-by: Mel Gorman <mgor...@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