Refactor dmu_object_alloc_dnsize() and dnode_hold_impl() to simplify the
code, fix errors introduced by commit dbeb879 (PR #6117) interacting
badly with large dnodes, and improve performance.
* When allocating a new dnode in dmu_object_alloc_dnsize(), update the
percpu object ID for the core's metadnode chunk immediately. This
eliminates most lock contention when taking the hold and creating the
dnode.
* Correct detection of the chunk boundary to work properly with large
dnodes.
* Separate the dmu_hold_impl() code for the FREE case from the code for
the ALLOCATED case to make it easier to read.
* Fully populate the dnode handle array immediately after reading a
block of the metadnode from disk. Subsequently the dnode handle array
provides enough information to determine which dnode slots are in use
and which are free.
* Add several kstats to allow the behavior of the code to be examined.
* Verify dnode packing in large_dnode_008_pos.ksh. Since the test is
purely creates, it should leave very few holes in the metadnode.
* Add test large_dnode_009_pos.ksh, which performs concurrent creates
and deletes, to complement existing test which does only creates.
With the above fixes, there is very little contention in a test of about
200,000 racing dnode allocations produced by tests 'large_dnode_008_pos'
and 'large_dnode_009_pos'.
name type data
dnode_hold_dbuf_hold 4 0
dnode_hold_dbuf_read 4 0
dnode_hold_alloc_hits 4 3804690
dnode_hold_alloc_misses 4 216
dnode_hold_alloc_interior 4 3
dnode_hold_alloc_lock_retry 4 0
dnode_hold_alloc_lock_misses 4 0
dnode_hold_alloc_type_none 4 0
dnode_hold_free_hits 4 203105
dnode_hold_free_misses 4 4
dnode_hold_free_lock_misses 4 0
dnode_hold_free_lock_retry 4 0
dnode_hold_free_overflow 4 0
dnode_hold_free_refcount 4 57
dnode_hold_free_txg 4 0
dnode_allocate 4 203154
dnode_reallocate 4 0
dnode_buf_evict 4 23918
dnode_alloc_next_chunk 4 4887
dnode_alloc_race 4 0
dnode_alloc_next_block 4 18
The performance is slightly improved for concurrent creates with
16+ threads, and unchanged for low thread counts.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Olaf Faaland <faaland1@llnl.gov>
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