diff options
| author | Alexander Motin <[email protected]> | 2024-05-01 13:59:32 -0400 |
|---|---|---|
| committer | Brian Behlendorf <[email protected]> | 2024-05-29 08:54:19 -0700 |
| commit | 672474659687115fc10f56f5473cd16eb307a99f (patch) | |
| tree | b96e56fae617b831916b5256ccb3b1db3e143a14 | |
| parent | 938d1588ebc7fb41e24500b2f21839f5a53b4ab5 (diff) | |
Slightly improve dnode hash
As I understand just for being less predictable dnode hash includes
8 bits of objset pointer, starting at 6. But since objset_t is
more than 1KB in size, its allocations are likely aligned to 2KB,
that means 11 lower bits provide no entropy. Just take the 8 bits
starting from 11.
Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Alexander Motin <[email protected]>
Sponsored by: iXsystems, Inc.
Closes #16131
| -rw-r--r-- | module/zfs/dmu_objset.c | 6 |
1 files changed, 3 insertions, 3 deletions
diff --git a/module/zfs/dmu_objset.c b/module/zfs/dmu_objset.c index ef966d670..c9729fd88 100644 --- a/module/zfs/dmu_objset.c +++ b/module/zfs/dmu_objset.c @@ -400,10 +400,10 @@ dnode_hash(const objset_t *os, uint64_t obj) ASSERT(zfs_crc64_table[128] == ZFS_CRC64_POLY); /* - * The low 6 bits of the pointer don't have much entropy, because - * the objset_t is larger than 2^6 bytes long. + * The lower 11 bits of the pointer don't have much entropy, because + * the objset_t is more than 1KB long and so likely aligned to 2KB. */ - crc = (crc >> 8) ^ zfs_crc64_table[(crc ^ (osv >> 6)) & 0xFF]; + crc = (crc >> 8) ^ zfs_crc64_table[(crc ^ (osv >> 11)) & 0xFF]; crc = (crc >> 8) ^ zfs_crc64_table[(crc ^ (obj >> 0)) & 0xFF]; crc = (crc >> 8) ^ zfs_crc64_table[(crc ^ (obj >> 8)) & 0xFF]; crc = (crc >> 8) ^ zfs_crc64_table[(crc ^ (obj >> 16)) & 0xFF]; |