[PATCH -mm 1/7] mm: thp: introduce __put_nontail_page()

[Oleg Nesterov <oleg@redhat.com>]

Add the new helper, __put_nontail_page(page), which simply does
compound/single put depending on PageHead(). put_compound_page()
can use it 3 times, probably it can have other users.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 mm/swap.c |   60 ++++++++++++++++++++++++++----------------------------------
 1 files changed, 26 insertions(+), 34 deletions(-)

diff --git a/mm/swap.c b/mm/swap.c
index 0040d9c..f83de1f 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -79,21 +79,26 @@ static void __put_compound_page(struct page *page)
 	(*dtor)(page);
 }
 
+static void __put_nontail_page(struct page *page)
+{
+	if (put_page_testzero(page)) {
+		/*
+		 * By the time all refcounts have been released
+		 * split_huge_page cannot run anymore from under us.
+		 */
+		if (PageHead(page))
+			__put_compound_page(page);
+		else
+			__put_single_page(page);
+	}
+}
+
 static void put_compound_page(struct page *page)
 {
 	struct page *page_head;
 
 	if (likely(!PageTail(page))) {
-		if (put_page_testzero(page)) {
-			/*
-			 * By the time all refcounts have been released
-			 * split_huge_page cannot run anymore from under us.
-			 */
-			if (PageHead(page))
-				__put_compound_page(page);
-			else
-				__put_single_page(page);
-		}
+		__put_nontail_page(page);
 		return;
 	}
 
@@ -176,24 +181,16 @@ static void put_compound_page(struct page *page)
 		if (unlikely(!PageTail(page))) {
 			/* __split_huge_page_refcount run before us */
 			compound_unlock_irqrestore(page_head, flags);
-			if (put_page_testzero(page_head)) {
-				/*
-				 * The head page may have been freed
-				 * and reallocated as a compound page
-				 * of smaller order and then freed
-				 * again.  All we know is that it
-				 * cannot have become: a THP page, a
-				 * compound page of higher order, a
-				 * tail page.  That is because we
-				 * still hold the refcount of the
-				 * split THP tail and page_head was
-				 * the THP head before the split.
-				 */
-				if (PageHead(page_head))
-					__put_compound_page(page_head);
-				else
-					__put_single_page(page_head);
-			}
+			/*
+			 * The head page may have been freed and reallocated
+			 * as a compound page of smaller order and then freed
+			 * again. All we know is that it cannot have become:
+			 * a THP page, a compound page of higher order, a tail
+			 * page. That is because we still hold the refcount of
+			 * the split THP tail and page_head was the THP head
+			 * before the split.
+			 */
+			__put_nontail_page(page_head);
 out_put_single:
 			if (put_page_testzero(page))
 				__put_single_page(page);
@@ -215,12 +212,7 @@ out_put_single:
 		VM_BUG_ON(atomic_read(&page->_count) != 0);
 		compound_unlock_irqrestore(page_head, flags);
 
-		if (put_page_testzero(page_head)) {
-			if (PageHead(page_head))
-				__put_compound_page(page_head);
-			else
-				__put_single_page(page_head);
-		}
+		__put_nontail_page(page_head);
 	} else {
 		/* page_head is a dangling pointer */
 		VM_BUG_ON(PageTail(page));
-- 
1.5.5.1