mm: page lock use lock bitops

trylock_page, unlock_page open and close a critical section. Hence,
we can use the lock bitops to get the desired memory ordering.

Also, mark trylock as likely to succeed (and remove the annotation from
callers).

Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 7 insertions, 10 deletions

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 7334b2b6c4c6..709742be02f0 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -311,7 +311,7 @@ static inline void __clear_page_locked(struct page *page)
 
 static inline int trylock_page(struct page *page)
 {
-        return !test_and_set_bit(PG_locked, &page->flags);
+        return (likely(!test_and_set_bit_lock(PG_locked, &page->flags)));
 }
 
 /*
diff --git a/mm/filemap.c b/mm/filemap.c
index a1ddd2557af2..e1b23fda48de 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -573,17 +573,14 @@ EXPORT_SYMBOL(wait_on_page_bit);
  * mechananism between PageLocked pages and PageWriteback pages is shared.
  * But that's OK - sleepers in wait_on_page_writeback() just go back to sleep.
  *
- * The first mb is necessary to safely close the critical section opened by the
- * test_and_set_bit() to lock the page; the second mb is necessary to enforce
- * ordering between the clear_bit and the read of the waitqueue (to avoid SMP
- * races with a parallel wait_on_page_locked()).
+ * The mb is necessary to enforce ordering between the clear_bit and the read
+ * of the waitqueue (to avoid SMP races with a parallel wait_on_page_locked()).
  */
 void unlock_page(struct page *page)
 {
-        smp_mb__before_clear_bit();
-        if (!test_and_clear_bit(PG_locked, &page->flags))
-                BUG();
-        smp_mb__after_clear_bit(); 
+        VM_BUG_ON(!PageLocked(page));
+        clear_bit_unlock(PG_locked, &page->flags);
+        smp_mb__after_clear_bit();
         wake_up_page(page, PG_locked);
 }
 EXPORT_SYMBOL(unlock_page);
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 2a97fafa3d89..90cb67a5417c 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -422,7 +422,7 @@ void free_swap_and_cache(swp_entry_t entry)
         if (p) {
                 if (swap_entry_free(p, swp_offset(entry)) == 1) {
                         page = find_get_page(&swapper_space, entry.val);
-                        if (page && unlikely(!trylock_page(page))) {
+                        if (page && !trylock_page(page)) {
                                 page_cache_release(page);
                                 page = NULL;
                         }