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Allow zero compression if dedup is enabled #17435
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Having high-refcount dedup entries for zero blocks is inefficient when they could be recorded as a holes instead. Normally, zero compression is not done if compression is disabled to not confuse naive benchmarks. But with dedup enabled, it is expected that the write will be skipped anyway, so we are just optimizing the way it is skipped. Signed-off-by: Alexander Motin <mav@FreeBSD.org> Sponsored by: iXsystems, Inc.
gmelikov
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+1 this way looks cleaner to me
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robn
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Jun 8, 2025
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Smooth.
behlendorf
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Jun 10, 2025
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Jun 13, 2025
Having high-refcount dedup entries for zero blocks is inefficient when they could be recorded as a holes instead. Normally, zero compression is not done if compression is disabled to not confuse naive benchmarks. But with dedup enabled, it is expected that the write will be skipped anyway, so we are just optimizing the way it is skipped. Reviewed-by: Rob Norris <robn@despairlabs.com> Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: George Melikov <mail@gmelikov.ru> Signed-off-by: Alexander Motin <mav@FreeBSD.org> Sponsored by: iXsystems, Inc. Closes openzfs#17435
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behlendorf
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Jun 17, 2025
Having high-refcount dedup entries for zero blocks is inefficient when they could be recorded as a holes instead. Normally, zero compression is not done if compression is disabled to not confuse naive benchmarks. But with dedup enabled, it is expected that the write will be skipped anyway, so we are just optimizing the way it is skipped. Reviewed-by: Rob Norris <robn@despairlabs.com> Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: George Melikov <mail@gmelikov.ru> Signed-off-by: Alexander Motin <mav@FreeBSD.org> Sponsored by: iXsystems, Inc. Closes #17435
behlendorf
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Jun 17, 2025
Having high-refcount dedup entries for zero blocks is inefficient when they could be recorded as a holes instead. Normally, zero compression is not done if compression is disabled to not confuse naive benchmarks. But with dedup enabled, it is expected that the write will be skipped anyway, so we are just optimizing the way it is skipped. Reviewed-by: Rob Norris <robn@despairlabs.com> Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: George Melikov <mail@gmelikov.ru> Signed-off-by: Alexander Motin <mav@FreeBSD.org> Sponsored by: iXsystems, Inc. Closes openzfs#17435
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Having high-refcount dedup entries for zero blocks is inefficient when they could be recorded as a holes instead. Normally, zero compression is not done if compression is disabled to not confuse naive benchmarks. But with dedup enabled, it is expected that the write will be skipped anyway, so we are just optimizing the way it is skipped.
This is an alternative approach to #17291, which I think is cleaner by keeping all compression decisions in the same place. Plus it checks not for dedup enabled for specific block, but for dedup enabled on dataset in general. Usually those are the same, except for ZIL writes, which are not dedupable now for technical reasons, but which would still benefit a lot from zero compression.
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