OpenZFS Lands A Very Nice Performance Optimization

A very nice feature pull request was merged to OpenZFS that can provide a nice performance improvement to this open-source ZFS file-system implementation to kick off the new year.

Alexander Motin with iXsystems has seen his uncached prefetch work land into OpenZFS. Motin summed up in the now-merged pull request:

This change gives ARC a knowledge about uncacheable buffers. It is passed to arc_read() and arc_write() and stored in ARC header. When remove_reference() drops last reference on the ARC header, it can either immediately destroy it, or if it is marked as prefetch, put it into new arc_uncached state. That state is scanned every second, looking for stale buffers that were not demand read (in which case they are evicted immediately).
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With the combination of enabled prefetch and avoided memory copy this change improves sequential single-threaded read speed from a wide NVMe pool from 2049 to 3932 MiB/s. During write profiler shows 22% reduction of unhalted CPU cycles at the same throughput of 3653 MiB/s.

OpenZFS developer Brian Behlendorf shared some benchmark results featuring this change and the performance there also looks very nice:

A nice way to start 2023 for OpenZFS... More details via this pull.