[PATCH] reduce number of parameters to __wait_on_bit() and __wait_on_bit_lock()

Some of the parameters to __wait_on_bit() and __wait_on_bit_lock() are
redundant, as the wait_bit_queue parameter holds the flags word and the bit
number.  This patch updates __wait_on_bit() and __wait_on_bit_lock() to
fetch that information from the wait_bit_queue passed to them and so reduce
the number of parameters so that -mregparm may be more effective.

Incremental atop the complete out-of-lining of the contention cases and the
fastcall and wait_on_bit_lock()/test_and_set_bit() fixes.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/fs-writeback.c

@@ -261,8 +261,8 @@ __writeback_single_inode(struct inode *inode,
 		do {
 			__iget(inode);
 			spin_unlock(&inode_lock);
-			__wait_on_bit(wqh, &wq, &inode->i_state, __I_LOCK,
-					inode_wait, TASK_UNINTERRUPTIBLE);
+			__wait_on_bit(wqh, &wq, inode_wait,
+							TASK_UNINTERRUPTIBLE);
 			iput(inode);
 			spin_lock(&inode_lock);
 		} while (inode->i_state & I_LOCK);

include/linux/wait.h

@@ -140,8 +140,8 @@ void FASTCALL(__wake_up(wait_queue_head_t *q, unsigned int mode, int nr, void *k
 extern void FASTCALL(__wake_up_locked(wait_queue_head_t *q, unsigned int mode));
 extern void FASTCALL(__wake_up_sync(wait_queue_head_t *q, unsigned int mode, int nr));
 void FASTCALL(__wake_up_bit(wait_queue_head_t *, void *, int));
-int FASTCALL(__wait_on_bit(wait_queue_head_t *, struct wait_bit_queue *, void *, int, int (*)(void *), unsigned));
-int FASTCALL(__wait_on_bit_lock(wait_queue_head_t *, struct wait_bit_queue *, void *, int, int (*)(void *), unsigned));
+int FASTCALL(__wait_on_bit(wait_queue_head_t *, struct wait_bit_queue *, int (*)(void *), unsigned));
+int FASTCALL(__wait_on_bit_lock(wait_queue_head_t *, struct wait_bit_queue *, int (*)(void *), unsigned));
 void FASTCALL(wake_up_bit(void *, int));
 int FASTCALL(out_of_line_wait_on_bit(void *, int, int (*)(void *), unsigned));
 int FASTCALL(out_of_line_wait_on_bit_lock(void *, int, int (*)(void *), unsigned));

kernel/wait.c

@@ -152,13 +152,15 @@ EXPORT_SYMBOL(wake_bit_function);
  */
 int __sched fastcall
 __wait_on_bit(wait_queue_head_t *wq, struct wait_bit_queue *q,
-		void *word, int bit, int (*action)(void *), unsigned mode)
+			int (*action)(void *), unsigned mode)
 {
 	int ret = 0;
 
+	do {
 		prepare_to_wait(wq, &q->wait, mode);
-	if (test_bit(bit, word))
-		ret = (*action)(word);
+		if (test_bit(q->key.bit_nr, q->key.flags))
+			ret = (*action)(q->key.flags);
+	} while (test_bit(q->key.bit_nr, q->key.flags) && !ret);
 	finish_wait(wq, &q->wait);
 	return ret;
 }
@@ -170,23 +172,23 @@ int __sched fastcall out_of_line_wait_on_bit(void *word, int bit,
 	wait_queue_head_t *wq = bit_waitqueue(word, bit);
 	DEFINE_WAIT_BIT(wait, word, bit);
 
-	return __wait_on_bit(wq, &wait, word, bit, action, mode);
+	return __wait_on_bit(wq, &wait, action, mode);
 }
 EXPORT_SYMBOL(out_of_line_wait_on_bit);
 
 int __sched fastcall
 __wait_on_bit_lock(wait_queue_head_t *wq, struct wait_bit_queue *q,
-		void *word, int bit, int (*action)(void *), unsigned mode)
+			int (*action)(void *), unsigned mode)
 {
 	int ret = 0;
 
 	do {
 		prepare_to_wait_exclusive(wq, &q->wait, mode);
-		if (test_bit(bit, word)) {
-			if ((ret = (*action)(word)))
+		if (test_bit(q->key.bit_nr, q->key.flags)) {
+			if ((ret = (*action)(q->key.flags)))
 				break;
 		}
-	} while (test_and_set_bit(bit, word));
+	} while (test_and_set_bit(q->key.bit_nr, q->key.flags));
 	finish_wait(wq, &q->wait);
 	return ret;
 }
@@ -198,7 +200,7 @@ int __sched fastcall out_of_line_wait_on_bit_lock(void *word, int bit,
 	wait_queue_head_t *wq = bit_waitqueue(word, bit);
 	DEFINE_WAIT_BIT(wait, word, bit);
 
-	return __wait_on_bit_lock(wq, &wait, word, bit, action, mode);
+	return __wait_on_bit_lock(wq, &wait, action, mode);
 }
 EXPORT_SYMBOL(out_of_line_wait_on_bit_lock);
 

mm/filemap.c

@@ -381,8 +381,8 @@ void fastcall wait_on_page_bit(struct page *page, int bit_nr)
 	DEFINE_WAIT_BIT(wait, &page->flags, bit_nr);
 
 	if (test_bit(bit_nr, &page->flags))
-		__wait_on_bit(page_waitqueue(page), &wait, wait.key.flags,
-				bit_nr, sync_page, TASK_UNINTERRUPTIBLE);
+		__wait_on_bit(page_waitqueue(page), &wait, sync_page,
+							TASK_UNINTERRUPTIBLE);
 }
 EXPORT_SYMBOL(wait_on_page_bit);
 
@@ -440,8 +440,8 @@ void fastcall __lock_page(struct page *page)
 {
 	DEFINE_WAIT_BIT(wait, &page->flags, PG_locked);
 
-	__wait_on_bit_lock(page_waitqueue(page), &wait, wait.key.flags,
-				PG_locked, sync_page, TASK_UNINTERRUPTIBLE);
+	__wait_on_bit_lock(page_waitqueue(page), &wait, sync_page,
+							TASK_UNINTERRUPTIBLE);
 }
 EXPORT_SYMBOL(__lock_page);