ceph: use __page_cache_alloc and add_to_page_cache_lru

Following Nick Piggin patches in btrfs, pagecache pages should be
allocated with __page_cache_alloc, so they obey pagecache memory
policies.

Also, using add_to_page_cache_lru instead of using a private
pagevec where applicable.

Signed-off-by: Yehuda Sadeh <yehuda@hq.newdream.net>
Signed-off-by: Sage Weil <sage@newdream.net>
diff --git a/fs/ceph/messenger.c b/fs/ceph/messenger.c
index cd4fadb..af3b143 100644
--- a/fs/ceph/messenger.c
+++ b/fs/ceph/messenger.c
@@ -1947,7 +1947,7 @@
 
 	/* the zero page is needed if a request is "canceled" while the message
 	 * is being written over the socket */
-	msgr->zero_page = alloc_page(GFP_KERNEL | __GFP_ZERO);
+	msgr->zero_page = __page_cache_alloc(GFP_KERNEL | __GFP_ZERO);
 	if (!msgr->zero_page) {
 		kfree(msgr);
 		return ERR_PTR(-ENOMEM);