thp: share get_huge_page_tail()

This avoids duplicating the function in every arch gup_fast.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <jweiner@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: David Gibson <david@gibson.dropbear.id.au>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: David Miller <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 11 insertions, 0 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index f81b7b41930c..3dc3a8c2c485 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -376,6 +376,17 @@ static inline int page_count(struct page *page)
         return atomic_read(&compound_head(page)->_count);
 }
 
+static inline void get_huge_page_tail(struct page *page)
+{
+        /*
+         * __split_huge_page_refcount() cannot run
+         * from under us.
+         */
+        VM_BUG_ON(page_mapcount(page) < 0);
+        VM_BUG_ON(atomic_read(&page->_count) != 0);
+        atomic_inc(&page->_mapcount);
+}
+
 extern bool __get_page_tail(struct page *page);
 
 static inline void get_page(struct page *page)