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MFC r357502: Few microoptimizations to dbuf layer.

Description

MFC r357502: Few microoptimizations to dbuf layer.

Move db_link into the same cache line as db_blkid and db_level.
It allows significantly reduce avl_add() time in dbuf_create() on
systems with large RAM and huge number of dbufs per dnode.

Avoid few accesses to dbuf_caches[].size, which is highly congested
under high IOPS and never stays in cache for a long time. Use local
value we are receiving from zfs_refcount_add_many() any way.

Remove cache_size_bytes_max bump from dbuf_evict_one(). I don't see
a point to do it on dbuf eviction after we done it on insertion in
dbuf_rele_and_unlock().

Details

Provenance
mavAuthored on
Parents
rS358059: MFC r357453: Unblock kstat.zfs.misc.dbufstats sysctls.
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