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Reduce dataset buffers re-dirtying

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For each block written or freed ZFS dirties ds_dbuf of the dataset.
While dbuf_dirty() has a fast path for already dirty dbufs, it still
require taking the lock and doing some things visible in profiler.

Investigation shown ds_dbuf dirtying by dsl_dataset_block_born()
and some of dsl_dataset_block_kill() are just not needed, since
by the time they are called in sync context the ds_dbuf is already
dirtied by dsl_dataset_sync().

Tests show this reducing large file deletion time by ~3% by saving
CPU time of single-threaded part of the sync thread.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Alexander Motin <alexander.motin@TrueNAS.com>
Closes #18028
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Alexander Motin 2025-12-09 12:18:09 -05:00 committed by GitHub
parent 574d5f3313
commit 09492e0f21
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1 changed files with 4 additions and 2 deletions
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6
module/zfs/dsl_dataset.c
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@ -161,7 +161,8 @@ dsl_dataset_block_born(dsl_dataset_t *ds, const blkptr_t *bp, dmu_tx_t *tx)
ASSERT3U(BP_GET_BIRTH(bp), >,
dsl_dataset_phys(ds)->ds_prev_snap_txg);
dmu_buf_will_dirty(ds->ds_dbuf, tx);
/* ds_dbuf is pre-dirtied in dsl_dataset_sync(). */
ASSERT(dmu_buf_is_dirty(ds->ds_dbuf, tx));
mutex_enter(&ds->ds_lock);
delta = parent_delta(ds, used);
dsl_dataset_phys(ds)->ds_referenced_bytes += used;
@ -274,7 +275,8 @@ dsl_dataset_block_kill(dsl_dataset_t *ds, const blkptr_t *bp, dmu_tx_t *tx,
ASSERT3P(tx->tx_pool, ==, ds->ds_dir->dd_pool);
ASSERT(!ds->ds_is_snapshot);
dmu_buf_will_dirty(ds->ds_dbuf, tx);
/* ds_dbuf is pre-dirtied in dsl_dataset_sync(). */
ASSERT(dmu_buf_is_dirty(ds->ds_dbuf, tx));
/*
* Track block for livelist, but ignore embedded blocks because