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Finally drop long disabled vdev cache.

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It was a vdev level read cache, designed to aggregate many small
reads by speculatively issuing bigger reads instead and caching
the result.  But since it has almost no idea about what is going
on with exception of ZIO_FLAG_DONT_CACHE flag set by higher layers,
it was found to make more harm than good, for which reason it was
disabled for the past 12 years.  These days we have much better
instruments to enlarge the I/Os, such as speculative and prescient
prefetches, I/O scheduler, I/O aggregation etc.

Besides just the dead code removal this removes one extra mutex
lock/unlock per write inside vdev_cache_write(), not otherwise
disabled and trying to do some work.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by:	Alexander Motin <mav@FreeBSD.org>
Sponsored by:	iXsystems, Inc.
Closes #14953
This commit is contained in:
Alexander Motin
2023-06-09 15:40:55 -04:00
committed by GitHub
parent 6db4ed51d6
commit 70ea484e3e
20 changed files with 13 additions and 562 deletions
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man/man8/zpool-events.8
-1
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@@ -456,7 +456,6 @@ ZIO_FLAG_CANFAIL:0x00000080
ZIO_FLAG_SPECULATIVE:0x00000100
ZIO_FLAG_CONFIG_WRITER:0x00000200
ZIO_FLAG_DONT_RETRY:0x00000400
ZIO_FLAG_DONT_CACHE:0x00000800
ZIO_FLAG_NODATA:0x00001000
ZIO_FLAG_INDUCE_DAMAGE:0x00002000