thp: add compound_trans_head() helper

Cleanup some code with common compound_trans_head helper.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <jweiner@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Avi Kivity <avi@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 12 deletions

diff --git a/mm/ksm.c b/mm/ksm.c
index 4d5a681923bb..33781de0b6bf 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -415,20 +415,11 @@ out:
 static struct page *page_trans_compound_anon(struct page *page)
 {
         if (PageTransCompound(page)) {
-                struct page *head;
-                head = compound_head(page);
+                struct page *head = compound_trans_head(page);
                 /*
-                 * head may be a dangling pointer.
-                 * __split_huge_page_refcount clears PageTail
-                 * before overwriting first_page, so if
-                 * PageTail is still there it means the head
-                 * pointer isn't dangling.
+                 * head may actually be splitted and freed from under
+                 * us but it's ok here.
                  */
-                if (head != page) {
-                        smp_rmb();
-                        if (!PageTransCompound(page))
-                                return NULL;
-                }
                 if (PageAnon(head))
                         return head;
         }