dm bufio: update comment in dm-bufio.c

* Hashtable has been replaced by rbtree to manage buffers.
  Update the comment.
* Fix typo in the comment for dm_bufio_issue_flush
Signed-off-by: Shenghui Wang <shhuiw@foxmail.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-bufio.c

@@ -65,7 +65,7 @@
 
 /*
  * Linking of buffers:
- *	All buffers are linked to cache_hash with their hash_list field.
+ *	All buffers are linked to buffer_tree with their node field.
  *
  *	Clean buffers that are not being written (B_WRITING not set)
  *	are linked to lru[LIST_CLEAN] with their lru_list field.
@@ -457,7 +457,7 @@ static void free_buffer(struct dm_buffer *b)
 }
 
 /*
- * Link buffer to the hash list and clean or dirty queue.
+ * Link buffer to the buffer tree and clean or dirty queue.
  */
 static void __link_buffer(struct dm_buffer *b, sector_t block, int dirty)
 {
@@ -472,7 +472,7 @@ static void __link_buffer(struct dm_buffer *b, sector_t block, int dirty)
 }
 
 /*
- * Unlink buffer from the hash list and dirty or clean queue.
+ * Unlink buffer from the buffer tree and dirty or clean queue.
  */
 static void __unlink_buffer(struct dm_buffer *b)
 {
@@ -993,7 +993,7 @@ static struct dm_buffer *__bufio_new(struct dm_bufio_client *c, sector_t block,
 
 	/*
 	 * We've had a period where the mutex was unlocked, so need to
-	 * recheck the hash table.
+	 * recheck the buffer tree.
 	 */
 	b = __find(c, block);
 	if (b) {
@@ -1327,7 +1327,7 @@ int dm_bufio_write_dirty_buffers(struct dm_bufio_client *c)
 EXPORT_SYMBOL_GPL(dm_bufio_write_dirty_buffers);
 
 /*
- * Use dm-io to send and empty barrier flush the device.
+ * Use dm-io to send an empty barrier to flush the device.
  */
 int dm_bufio_issue_flush(struct dm_bufio_client *c)
 {
@@ -1356,7 +1356,7 @@ EXPORT_SYMBOL_GPL(dm_bufio_issue_flush);
  * Then, we write the buffer to the original location if it was dirty.
  *
  * Then, if we are the only one who is holding the buffer, relink the buffer
- * in the hash queue for the new location.
+ * in the buffer tree for the new location.
  *
  * If there was someone else holding the buffer, we write it to the new
  * location but not relink it, because that other user needs to have the buffer