thp: compound_trans_order

Read compound_trans_order safe. Noop for CONFIG_TRANSPARENT_HUGEPAGE=n.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 14 insertions, 0 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 9c2695beab86..ce97a2bb0b19 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -450,6 +450,20 @@ static inline int compound_order(struct page *page)
         return (unsigned long)page[1].lru.prev;
 }
 
+static inline int compound_trans_order(struct page *page)
+{
+        int order;
+        unsigned long flags;
+
+        if (!PageHead(page))
+                return 0;
+
+        flags = compound_lock_irqsave(page);
+        order = compound_order(page);
+        compound_unlock_irqrestore(page, flags);
+        return order;
+}
+
 static inline void set_compound_order(struct page *page, unsigned long order)
 {
         page[1].lru.prev = (void *)order;