mm: use refcounts for page_lock_anon_vma()

Convert page_lock_anon_vma() over to use refcounts.  This is done to
prepare for the conversion of anon_vma from spinlock to mutex.

Sadly this inceases the cost of page_lock_anon_vma() from one to two
atomics, a follow up patch addresses this, lets keep that simple for now.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Acked-by: Hugh Dickins <hughd@google.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: David Miller <davem@davemloft.net>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Nick Piggin <npiggin@kernel.dk>
Cc: Namhyung Kim <namhyung@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 13 deletions

diff --git a/mm/migrate.c b/mm/migrate.c
index 34132f8e910..e4a5c912983 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -721,15 +721,11 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
 		 * Only page_lock_anon_vma() understands the subtleties of
 		 * getting a hold on an anon_vma from outside one of its mms.
 		 */
-		anon_vma = page_lock_anon_vma(page);
+		anon_vma = page_get_anon_vma(page);
 		if (anon_vma) {
 			/*
-			 * Take a reference count on the anon_vma if the
-			 * page is mapped so that it is guaranteed to
-			 * exist when the page is remapped later
+			 * Anon page
 			 */
-			get_anon_vma(anon_vma);
-			page_unlock_anon_vma(anon_vma);
 		} else if (PageSwapCache(page)) {
 			/*
 			 * We cannot be sure that the anon_vma of an unmapped
@@ -857,13 +853,8 @@ static int unmap_and_move_huge_page(new_page_t get_new_page,
 		lock_page(hpage);
 	}
 
-	if (PageAnon(hpage)) {
-		anon_vma = page_lock_anon_vma(hpage);
-		if (anon_vma) {
-			get_anon_vma(anon_vma);
-			page_unlock_anon_vma(anon_vma);
-		}
-	}
+	if (PageAnon(hpage))
+		anon_vma = page_get_anon_vma(hpage);
 
 	try_to_unmap(hpage, TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);