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>
diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index bddfba1..8e6c8c4 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -126,6 +126,23 @@
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 @@
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)
{