---

yaml
---
r: 142627
b: refs/heads/master
c: 047180f
h: refs/heads/master
i:
  142625: 8e101d4
  142623: ca9d1a5
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 47420c799830d4676e544dbec56b2a7f787528f5
+refs/heads/master: 047180f2d7bf95ff5699ca04da639a7556e23435

trunk/fs/nilfs2/gcinode.c

@@ -1,5 +1,5 @@
 /*
- * gcinode.c - NILFS memory inode for GC
+ * gcinode.c - dummy inodes to buffer blocks for garbage collection
  *
  * Copyright (C) 2005-2008 Nippon Telegraph and Telephone Corporation.
  *
@@ -22,6 +22,25 @@
  * Revised by Ryusuke Konishi <ryusuke@osrg.net>.
  *
  */
+/*
+ * This file adds the cache of on-disk blocks to be moved in garbage
+ * collection.  The disk blocks are held with dummy inodes (called
+ * gcinodes), and this file provides lookup function of the dummy
+ * inodes and their buffer read function.
+ *
+ * Since NILFS2 keeps up multiple checkpoints/snapshots accross GC, it
+ * has to treat blocks that belong to a same file but have different
+ * checkpoint numbers.  To avoid interference among generations, dummy
+ * inodes are managed separatly from actual inodes, and their lookup
+ * function (nilfs_gc_iget) is designed to be specified with a
+ * checkpoint number argument as well as an inode number.
+ *
+ * Buffers and pages held by the dummy inodes will be released each
+ * time after they are copied to a new log.  Dirty blocks made on the
+ * current generation and the blocks to be moved by GC never overlap
+ * because the dirty blocks make a new generation; they rather must be
+ * written individually.
+ */
 
 #include <linux/buffer_head.h>
 #include <linux/mpage.h>