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
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051460b8b2
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8fd3a5d02f
module/zfs
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@ -400,10 +400,10 @@ dnode_hash(const objset_t *os, uint64_t obj)
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ASSERT(zfs_crc64_table[128] == ZFS_CRC64_POLY);
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ASSERT(zfs_crc64_table[128] == ZFS_CRC64_POLY);
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/*
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/*
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* The low 6 bits of the pointer don't have much entropy, because
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* The lower 11 bits of the pointer don't have much entropy, because
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* the objset_t is larger than 2^6 bytes long.
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* the objset_t is more than 1KB long and so likely aligned to 2KB.
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*/
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*/
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crc = (crc >> 8) ^ zfs_crc64_table[(crc ^ (osv >> 6)) & 0xFF];
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crc = (crc >> 8) ^ zfs_crc64_table[(crc ^ (osv >> 11)) & 0xFF];
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crc = (crc >> 8) ^ zfs_crc64_table[(crc ^ (obj >> 0)) & 0xFF];
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crc = (crc >> 8) ^ zfs_crc64_table[(crc ^ (obj >> 0)) & 0xFF];
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crc = (crc >> 8) ^ zfs_crc64_table[(crc ^ (obj >> 8)) & 0xFF];
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crc = (crc >> 8) ^ zfs_crc64_table[(crc ^ (obj >> 8)) & 0xFF];
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crc = (crc >> 8) ^ zfs_crc64_table[(crc ^ (obj >> 16)) & 0xFF];
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crc = (crc >> 8) ^ zfs_crc64_table[(crc ^ (obj >> 16)) & 0xFF];
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