- * If the running transaction is the one containing
- * "add to orphan" operation (b_next_transaction !=
- * NULL), we have to wait for that transaction to
- * commit before we can really get rid of the buffer.
- * So just clear b_modified to not confuse transaction
- * credit accounting and refile the buffer to
- * BJ_Forget of the running transaction. If the just
- * committed transaction contains "add to orphan"
- * operation, we can completely invalidate the buffer
- * now. We are rather through in that since the
- * buffer may be still accessible when blocksize <
- * pagesize and it is attached to the last partial
- * page.
+ * Block device buffers need to stay mapped all the
+ * time, so it is enough to clear buffer_jbddirty and
+ * buffer_freed bits. For the file mapping buffers (i.e.
+ * journalled data) we need to unmap buffer and clear
+ * more bits. We also need to be careful about the check
+ * because the data page mapping can get cleared under
+ * our hands. Note that if mapping == NULL, we don't
+ * need to make buffer unmapped because the page is
+ * already detached from the mapping and buffers cannot
+ * get reused.