+ * Various log reservation values.
+ *
+ * These are based on the size of the file system block because that is what
+ * most transactions manipulate. Each adds in an additional 128 bytes per
+ * item logged to try to account for the overhead of the transaction mechanism.
+ *
+ * Note: Most of the reservations underestimate the number of allocation
+ * groups into which they could free extents in the xfs_bmap_finish() call.
+ * This is because the number in the worst case is quite high and quite
+ * unusual. In order to fix this we need to change xfs_bmap_finish() to free
+ * extents in only a single AG at a time. This will require changes to the
+ * EFI code as well, however, so that the EFI for the extents not freed is
+ * logged again in each transaction. See SGI PV #261917.
+ *
+ * Reservation functions here avoid a huge stack in xfs_trans_init due to
+ * register overflow from temporaries in the calculations.
+ */
+
+
+/*
+ * In a write transaction we can allocate a maximum of 2
+ * extents. This gives:
+ * the inode getting the new extents: inode size
+ * the inode's bmap btree: max depth * block size
+ * the agfs of the ags from which the extents are allocated: 2 * sector
+ * the superblock free block counter: sector size
+ * the allocation btrees: 2 exts * 2 trees * (2 * max depth - 1) * block size
+ * And the bmap_finish transaction can free bmap blocks in a join:
+ * the agfs of the ags containing the blocks: 2 * sector size
+ * the agfls of the ags containing the blocks: 2 * sector size
+ * the super block free block counter: sector size
+ * the allocation btrees: 2 exts * 2 trees * (2 * max depth - 1) * block size