nilfs2: add sync_page method to page caches of meta data

This applies block_sync_page() function to the sync_page method of
page caches for meta data files, gc page caches, and btree node
buffers.  This is a companion patch of ("nilfs2: enable sync_page
mothod") which applied the function for data pages.

This allows lock_page() for those meta data to unplug pending bio
requests.
Signed-off-by: NRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

fs/nilfs2/btnode.c

@@ -46,7 +46,9 @@ void nilfs_btnode_cache_init_once(struct address_space *btnc)
 	INIT_LIST_HEAD(&btnc->i_mmap_nonlinear);
 }
 
-static struct address_space_operations def_btnode_aops;
+static struct address_space_operations def_btnode_aops = {
+	.sync_page		= block_sync_page,
+};
 
 void nilfs_btnode_cache_init(struct address_space *btnc,
 			     struct backing_dev_info *bdi)

fs/nilfs2/gcinode.c

@@ -52,8 +52,9 @@
 #include "dat.h"
 #include "ifile.h"
 
-static struct address_space_operations def_gcinode_aops = {};
-/* XXX need def_gcinode_iops/fops? */
+static struct address_space_operations def_gcinode_aops = {
+	.sync_page		= block_sync_page,
+};
 
 /*
  * nilfs_gccache_submit_read_data() - add data buffer and submit read request

fs/nilfs2/mdt.c

@@ -430,6 +430,7 @@ nilfs_mdt_write_page(struct page *page, struct writeback_control *wbc)
 
 static struct address_space_operations def_mdt_aops = {
 	.writepage		= nilfs_mdt_write_page,
+	.sync_page		= block_sync_page,
 };
 
 static struct inode_operations def_mdt_iops;