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/file.c b/fs/ceph/file.c
index ed6f197..6230c3d 100644
--- a/fs/ceph/file.c
+++ b/fs/ceph/file.c
@@ -326,7 +326,7 @@
 	if (!pages)
 		return ERR_PTR(-ENOMEM);
 	for (i = 0; i < num_pages; i++) {
-		pages[i] = alloc_page(GFP_NOFS);
+		pages[i] = __page_cache_alloc(GFP_NOFS);
 		if (pages[i] == NULL) {
 			ceph_release_page_vector(pages, i);
 			return ERR_PTR(-ENOMEM);