From: Nick Piggin <npiggin@suse.de>
Date: Sun, 19 Oct 2008 03:26:59 +0000 (-0700)
Subject: mm: page lock use lock bitops
X-Git-Tag: v2.6.28-rc1~218
X-Git-Url: http://ftp.safe.ca/?p=safe%2Fjmp%2Flinux-2.6;a=commitdiff_plain;h=8413ac9d8c9a1366a4f57880723126cd24e5a5c3

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>
---

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 7334b2b..709742b 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 a1ddd25..e1b23fd 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 2a97faf..90cb67a 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;
 			}