Commit df3954ff authored by Darrick J. Wong's avatar Darrick J. Wong Committed by Dave Chinner

xfs: increase XFS_BTREE_MAXLEVELS to fit the rmapbt

By my calculations, a 1,073,741,824 block AG with a 1k block size
can attain a maximum height of 9.  Assuming a record size of 24
bytes, a key/ptr size of 44 bytes, and half-full btree nodes, we'd
need 53,687,092 blocks for the records and ~6 million blocks for the
keys.  That requires a btree of height 9 based on the following
derivation:

Block size = 1024b
sblock CRC header = 56b
== 1024-56 = 968 bytes for tree data

rmapbt record = 24b
== 40 records per leaf block

rmapbt ptr/key = 44b
== 22 ptr/keys per block

Worst case, each block is half full, so 20 records and 11 ptrs per block.

1073741824 rmap records / 20 records per block
== 53687092 leaf blocks

53687092 leaves / 11 ptrs per block
== 4880645 level 1 blocks
== 443695 level 2 blocks
== 40336 level 3 blocks
== 3667 level 4 blocks
== 334 level 5 blocks
== 31 level 6 blocks
== 3 level 7 blocks
== 1 level 8 block
Signed-off-by: default avatarDarrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: default avatarBrian Foster <bfoster@redhat.com>
Signed-off-by: default avatarDave Chinner <david@fromorbit.com>
parent ba9e7802
...@@ -133,7 +133,7 @@ do { \ ...@@ -133,7 +133,7 @@ do { \
} \ } \
} while (0) } while (0)
#define XFS_BTREE_MAXLEVELS 8 /* max of all btrees */ #define XFS_BTREE_MAXLEVELS 9 /* max of all btrees */
struct xfs_btree_ops { struct xfs_btree_ops {
/* size of the key and record structures */ /* size of the key and record structures */
......
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