fs/9p: set default readahead pages in cached mode

We want to enable readahead in cached mode
Signed-off-by: NAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: NVenkateswararao Jujjuri <jvrao@linux.vnet.ibm.com>
Signed-off-by: NEric Van Hensbergen <ericvh@gmail.com>

fs/9p/vfs_super.c

@@ -86,6 +86,8 @@ v9fs_fill_super(struct super_block *sb, struct v9fs_session_info *v9ses,
 	} else
 		sb->s_op = &v9fs_super_ops;
 	sb->s_bdi = &v9ses->bdi;
+	if (v9ses->cache)
+		sb->s_bdi->ra_pages = (VM_MAX_READAHEAD * 1024)/PAGE_CACHE_SIZE;
 
 	sb->s_flags = flags | MS_ACTIVE | MS_DIRSYNC | MS_NOATIME;
 	if (!v9ses->cache)