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Initialize vr_last_txg for rebuild - #18482
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Only call txg_wait_synced() when rebuild IOs were issued for this metaslab. This is a small optimization since in practice the first metaslab is very likely to have allocations and cause vr_last_txg to be initialized. After this point when processing empty metaslabs txg_wait_synced() is called but with an already committed txg so it will not wait. Still it's better not to call txg_wait_synced() at all when it's not needed. Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
amotin
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May 1, 2026
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Pull request overview
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This PR aims to avoid unnecessary txg_wait_synced() calls during vdev rebuild by only waiting when rebuild I/Os have actually set vr_last_txg.
Changes:
- Initialize
vr_last_txgto0when starting the rebuild thread. - Guard
txg_wait_synced()so it’s only called whenvr_last_txghas been set.
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andriytk
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May 1, 2026
behlendorf
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Status: Accepted
tonyhutter
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May 4, 2026
Only call txg_wait_synced() when rebuild IOs were issued for this metaslab. This is a small optimization since in practice the first metaslab is very likely to have allocations and cause vr_last_txg to be initialized. After this point when processing empty metaslabs txg_wait_synced() is called but with an already committed txg so it will not wait. Still it's better not to call txg_wait_synced() at all when it's not needed. Reviewed-by: Andriy Tkachuk <atkachuk@wasabi.com> Reviewed-by: Alexander Motin <alexander.motin@TrueNAS.com> Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Closes openzfs#18482
tonyhutter
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May 4, 2026
Only call txg_wait_synced() when rebuild IOs were issued for this metaslab. This is a small optimization since in practice the first metaslab is very likely to have allocations and cause vr_last_txg to be initialized. After this point when processing empty metaslabs txg_wait_synced() is called but with an already committed txg so it will not wait. Still it's better not to call txg_wait_synced() at all when it's not needed. Reviewed-by: Andriy Tkachuk <atkachuk@wasabi.com> Reviewed-by: Alexander Motin <alexander.motin@TrueNAS.com> Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Closes openzfs#18482
tonyhutter
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May 6, 2026
Only call txg_wait_synced() when rebuild IOs were issued for this metaslab. This is a small optimization since in practice the first metaslab is very likely to have allocations and cause vr_last_txg to be initialized. After this point when processing empty metaslabs txg_wait_synced() is called but with an already committed txg so it will not wait. Still it's better not to call txg_wait_synced() at all when it's not needed. Reviewed-by: Andriy Tkachuk <atkachuk@wasabi.com> Reviewed-by: Alexander Motin <alexander.motin@TrueNAS.com> Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Closes openzfs#18482
kithrup
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May 7, 2026
Only call txg_wait_synced() when rebuild IOs were issued for this metaslab. This is a small optimization since in practice the first metaslab is very likely to have allocations and cause vr_last_txg to be initialized. After this point when processing empty metaslabs txg_wait_synced() is called but with an already committed txg so it will not wait. Still it's better not to call txg_wait_synced() at all when it's not needed. Reviewed-by: Andriy Tkachuk <atkachuk@wasabi.com> Reviewed-by: Alexander Motin <alexander.motin@TrueNAS.com> Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Closes openzfs#18482
Gality369
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May 12, 2026
Only call txg_wait_synced() when rebuild IOs were issued for this metaslab. This is a small optimization since in practice the first metaslab is very likely to have allocations and cause vr_last_txg to be initialized. After this point when processing empty metaslabs txg_wait_synced() is called but with an already committed txg so it will not wait. Still it's better not to call txg_wait_synced() at all when it's not needed. Reviewed-by: Andriy Tkachuk <atkachuk@wasabi.com> Reviewed-by: Alexander Motin <alexander.motin@TrueNAS.com> Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Closes openzfs#18482
lundman
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Jul 30, 2026
Only call txg_wait_synced() when rebuild IOs were issued for this metaslab. This is a small optimization since in practice the first metaslab is very likely to have allocations and cause vr_last_txg to be initialized. After this point when processing empty metaslabs txg_wait_synced() is called but with an already committed txg so it will not wait. Still it's better not to call txg_wait_synced() at all when it's not needed. Reviewed-by: Andriy Tkachuk <atkachuk@wasabi.com> Reviewed-by: Alexander Motin <alexander.motin@TrueNAS.com> Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Closes openzfs#18482
pull Bot
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Sep 26, 2026
Only call txg_wait_synced() when rebuild IOs were issued for this metaslab. This is a small optimization since in practice the first metaslab is very likely to have allocations and cause vr_last_txg to be initialized. After this point when processing empty metaslabs txg_wait_synced() is called but with an already committed txg so it will not wait. Still it's better not to call txg_wait_synced() at all when it's not needed. Reviewed-by: Andriy Tkachuk <atkachuk@wasabi.com> Reviewed-by: Alexander Motin <alexander.motin@TrueNAS.com> Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Closes openzfs#18482
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Motivation and Context
Minor optimization as a followup to #18473.
Description
Only call txg_wait_synced() when rebuild IOs were issued for this metaslab. This is a small optimization since in practice the first metaslab is very likely to have allocations and cause vr_last_txg to be initialized. After this point when processing empty metaslabs txg_wait_synced() is called but with an already committed txg so it will not wait. Still it's better not to call txg_wait_synced() at all when it's not needed.
How Has This Been Tested?
Compiled, will be tested by the CI along with additional local testing.
Types of changes