[PATCH] find_lock_page(): call __lock_page() directly.

As find_lock_page() already checks with TestSetPageLocked() that page is
locked, there is no need to call lock_page() that will try-lock page again
(chances of page being unlocked in between are small).  Call __lock_page()
directly, this saves one atomic operation.

Also, mark truncate-while-slept path as unlikely while we are here.

(akpm: ug.  But this is actually a common path for normal old read()s against
a page which is under readahead I/O so ho-hum.)
Signed-off-by: NNikita Danilov <danilov@gmail.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

mm/filemap.c

@@ -555,11 +555,12 @@ struct page *find_lock_page(struct address_space *mapping,
 		page_cache_get(page);
 		if (TestSetPageLocked(page)) {
 			read_unlock_irq(&mapping->tree_lock);
-			lock_page(page);
+			__lock_page(page);
 			read_lock_irq(&mapping->tree_lock);
 
 			/* Has the page been truncated while we slept? */
-			if (page->mapping != mapping || page->index != offset) {
+			if (unlikely(page->mapping != mapping ||
+				     page->index != offset)) {
 				unlock_page(page);
 				page_cache_release(page);
 				goto repeat;