Alexander Motin ed2f7ba08d Implement uncached prefetch ... Previously the primarycache property was handled only in the dbuf layer. Since the speculative prefetcher is implemented in the ARC, it had to be disabled for uncacheable buffers. This change gives the ARC knowledge about uncacheable buffers via arc_read() and arc_write(). So when remove_reference() drops the last reference on the ARC header, it can either immediately destroy it, or if it is marked as prefetch, put it into a new arc_uncached state. That state is scanned every second, evicting stale buffers that were not demand read. This change also tracks dbufs that were read from the beginning, but not to the end. It is assumed that such buffers may receive further reads, and so they are stored in dbuf cache. If a following reads reaches the end of the buffer, it is immediately evicted. Otherwise it will follow regular dbuf cache eviction. Since the dbuf layer does not know actual file sizes, this logic is not applied to the final buffer of a dnode. Since uncacheable buffers should no longer stay in the ARC for long, this patch also tries to optimize I/O by allocating ARC physical buffers as linear to allow buffer sharing. Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: George Wilson <george.wilson@delphix.com> Reviewed-by: Ryan Moeller <ryan@iXsystems.com> Signed-off-by: Alexander Motin <mav@FreeBSD.org> Sponsored by: iXsystems, Inc. Closes #14243		2023-01-04 17:29:54 -07:00
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spl	Restrict visibility of per-dataset kstats inside FreeBSD jails	2022-12-09 11:04:29 -08:00
zfs	Implement uncached prefetch	2023-01-04 17:29:54 -07:00