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| author | Alexander Motin <mav@FreeBSD.org> | 2024-05-01 17:59:32 +0000 |
|---|---|---|
| committer | GitHub <noreply@github.com> | 2024-05-01 17:59:32 +0000 |
| commit | 8fd3a5d02f3f6bad9e8e65b6aded694eae222bf2 (patch) | |
| tree | c9fd8d33730defe4b95d744bbe4fef4a6dc9a42f | |
| parent | 051460b8b2bb78add2b7ed5255f7656a33be903a (diff) | |
| download | src-8fd3a5d02f3f6bad9e8e65b6aded694eae222bf2.tar.gz src-8fd3a5d02f3f6bad9e8e65b6aded694eae222bf2.zip | |
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 <behlendorf1@llnl.gov>
Signed-off-by: Alexander Motin <mav@FreeBSD.org>
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 2ba26f68e398..5ea99f742810 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]; |