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, 18 insertions, 0 deletions

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index bddfba1d7b85..8e6c8c42bc3c 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -126,6 +126,23 @@ static inline int hpage_nr_pages(struct page *page)
                 return HPAGE_PMD_NR;
         return 1;
 }
+static inline struct page *compound_trans_head(struct page *page)
+{
+        if (PageTail(page)) {
+                struct page *head;
+                head = page->first_page;
+                smp_rmb();
+                /*
+                 * 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.
+                 */
+                if (PageTail(page))
+                        return head;
+        }
+        return page;
+}
 #else /* CONFIG_TRANSPARENT_HUGEPAGE */
 #define HPAGE_PMD_SHIFT ({ BUG(); 0; })
 #define HPAGE_PMD_MASK ({ BUG(); 0; })
@@ -144,6 +161,7 @@ static inline int split_huge_page(struct page *page)
         do { } while (0)
 #define wait_split_huge_page(__anon_vma, __pmd) \
         do { } while (0)
+#define compound_trans_head(page) compound_head(page)
 static inline int hugepage_madvise(struct vm_area_struct *vma,
                                    unsigned long *vm_flags, int advice)
 {