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Remove fastwrite mechanism. #15107

Merged
merged 1 commit into from
Jul 28, 2023
Merged

Remove fastwrite mechanism. #15107

merged 1 commit into from
Jul 28, 2023

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amotin
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@amotin amotin commented Jul 25, 2023 •
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Fastwrite was introduced many years ago at 920dd52 to improve ZIL writes spread between multiple top-level vdevs by tracking number of allocated but not written blocks and choosing vdev with smaller count. It suposed to reduce ZIL knowledge about allocation, but actually made ZIL to even more actively report allocation code about the allocations, complicating both ZIL and metaslabs code.

On top of that, it seems ZIO_FLAG_FASTWRITE setting in dmu_sync() was lost many years ago, that was one of the declared benefits. Plus introduction of embedded log metaslab class solved another problem with allocation rotor accounting both normal and log allocations, since in most cases those are now in different metaslab classes.

After all that, I'd prefer to simplify already too complicated ZIL, ZIO and metaslab code if the benefit of complexity is not obvious.

Types of changes

  • Bug fix (non-breaking change which fixes an issue)
  • New feature (non-breaking change which adds functionality)
  • Performance enhancement (non-breaking change which improves efficiency)
  • Code cleanup (non-breaking change which makes code smaller or more readable)
  • Breaking change (fix or feature that would cause existing functionality to change)
  • Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
  • Documentation (a change to man pages or other documentation)

Checklist:

@amotin
Remove fastwrite mechanism.
43b694c 
Fastwrite was introduced many years ago to improve ZIL writes spread
between multiple top-level vdevs by tracking number of allocated but
not written blocks and choosing vdev with smaller count.  It suposed
to reduce ZIL knowledge about allocation, but actually made ZIL to
even more actively report allocation code about the allocations,
complicating both ZIL and metaslabs code.

On top of that, it seems ZIO_FLAG_FASTWRITE setting in dmu_sync()
was lost many years ago, that was one of the declared benefits. Plus
introduction of embedded log metaslab class solved another problem
with allocation rotor accounting both normal and log allocations,
since in most cases those are now in different metaslab classes.

After all that, I'd prefer to simplify already too complicated ZIL,
ZIO and metaslab code if the benefit of complexity is not obvious.

Signed-off-by:	Alexander Motin <[email protected]>
Sponsored by:	iXsystems, Inc.
@behlendorf behlendorf added the Status: Code Review Needed Ready for review and testing label Jul 25, 2023
@behlendorf behlendorf added Status: Accepted Ready to integrate (reviewed, tested) and removed Status: Code Review Needed Ready for review and testing labels Jul 28, 2023
@behlendorf behlendorf merged commit b22bab2 into openzfs:master Jul 28, 2023
14 of 15 checks passed
amotin added a commit to amotin/zfs that referenced this pull request Aug 25, 2023
@amotin
Remove fastwrite mechanism.
646339c 
Fastwrite was introduced many years ago to improve ZIL writes spread
between multiple top-level vdevs by tracking number of allocated but
not written blocks and choosing vdev with smaller count.  It suposed
to reduce ZIL knowledge about allocation, but actually made ZIL to
even more actively report allocation code about the allocations,
complicating both ZIL and metaslabs code.

On top of that, it seems ZIO_FLAG_FASTWRITE setting in dmu_sync()
was lost many years ago, that was one of the declared benefits. Plus
introduction of embedded log metaslab class solved another problem
with allocation rotor accounting both normal and log allocations,
since in most cases those are now in different metaslab classes.

After all that, I'd prefer to simplify already too complicated ZIL,
ZIO and metaslab code if the benefit of complexity is not obvious.

Reviewed-by: Brian Behlendorf <[email protected]>
Reviewed-by: George Wilson <[email protected]>
Signed-off-by:	Alexander Motin <[email protected]>
Sponsored by:	iXsystems, Inc.
Closes openzfs#15107
behlendorf pushed a commit that referenced this pull request Aug 25, 2023
@amotin @behlendorf
Remove fastwrite mechanism.
ffaedf0 
Fastwrite was introduced many years ago to improve ZIL writes spread
between multiple top-level vdevs by tracking number of allocated but
not written blocks and choosing vdev with smaller count.  It suposed
to reduce ZIL knowledge about allocation, but actually made ZIL to
even more actively report allocation code about the allocations,
complicating both ZIL and metaslabs code.

On top of that, it seems ZIO_FLAG_FASTWRITE setting in dmu_sync()
was lost many years ago, that was one of the declared benefits. Plus
introduction of embedded log metaslab class solved another problem
with allocation rotor accounting both normal and log allocations,
since in most cases those are now in different metaslab classes.

After all that, I'd prefer to simplify already too complicated ZIL,
ZIO and metaslab code if the benefit of complexity is not obvious.

Reviewed-by: Brian Behlendorf <[email protected]>
Reviewed-by: George Wilson <[email protected]>
Signed-off-by:	Alexander Motin <[email protected]>
Sponsored by:	iXsystems, Inc.
Closes #15107
lundman pushed a commit to openzfsonwindows/openzfs that referenced this pull request Dec 12, 2023
@amotin @lundman
Remove fastwrite mechanism.
b510ace 
Fastwrite was introduced many years ago to improve ZIL writes spread
between multiple top-level vdevs by tracking number of allocated but
not written blocks and choosing vdev with smaller count.  It suposed
to reduce ZIL knowledge about allocation, but actually made ZIL to
even more actively report allocation code about the allocations,
complicating both ZIL and metaslabs code.

On top of that, it seems ZIO_FLAG_FASTWRITE setting in dmu_sync()
was lost many years ago, that was one of the declared benefits. Plus
introduction of embedded log metaslab class solved another problem
with allocation rotor accounting both normal and log allocations,
since in most cases those are now in different metaslab classes.

After all that, I'd prefer to simplify already too complicated ZIL,
ZIO and metaslab code if the benefit of complexity is not obvious.

Reviewed-by: Brian Behlendorf <[email protected]>
Reviewed-by: George Wilson <[email protected]>
Signed-off-by:	Alexander Motin <[email protected]>
Sponsored by:	iXsystems, Inc.
Closes openzfs#15107
@amotin amotin deleted the no_fastwrite branch March 22, 2024 16:36
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@grwilson grwilson grwilson approved these changes

@behlendorf behlendorf behlendorf approved these changes

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@amotin @behlendorf @grwilson