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