mm: spinlock tree_lock

mapping->tree_lock has no read lockers.  convert the lock from an rwlock
to a spinlock.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Hugh Dickins <hugh@veritas.com>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Reviewed-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 6 deletions

diff --git a/mm/migrate.c b/mm/migrate.c
index 3ca6392e82cc..153572fb60b8 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -323,7 +323,7 @@ static int migrate_page_move_mapping(struct address_space *mapping,
                 return 0;
         }
 
-        write_lock_irq(&mapping->tree_lock);
+        spin_lock_irq(&mapping->tree_lock);
 
         pslot = radix_tree_lookup_slot(&mapping->page_tree,
                                         page_index(page));
@@ -331,12 +331,12 @@ static int migrate_page_move_mapping(struct address_space *mapping,
         expected_count = 2 + !!PagePrivate(page);
         if (page_count(page) != expected_count ||
                         (struct page *)radix_tree_deref_slot(pslot) != page) {
-                write_unlock_irq(&mapping->tree_lock);
+                spin_unlock_irq(&mapping->tree_lock);
                 return -EAGAIN;
         }
 
         if (!page_freeze_refs(page, expected_count)) {
-                write_unlock_irq(&mapping->tree_lock);
+                spin_unlock_irq(&mapping->tree_lock);
                 return -EAGAIN;
         }
 
@@ -373,10 +373,9 @@ static int migrate_page_move_mapping(struct address_space *mapping,
         __dec_zone_page_state(page, NR_FILE_PAGES);
         __inc_zone_page_state(newpage, NR_FILE_PAGES);
 
-        write_unlock_irq(&mapping->tree_lock);
-        if (!PageSwapCache(newpage)) {
+        spin_unlock_irq(&mapping->tree_lock);
+        if (!PageSwapCache(newpage))
                 mem_cgroup_uncharge_cache_page(page);
-        }
 
         return 0;
 }