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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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include/sys/vdev.h
-6
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@@ -158,12 +158,6 @@ extern boolean_t vdev_allocatable(vdev_t *vd);
extern boolean_t vdev_accessible(vdev_t *vd, zio_t *zio);
extern boolean_t vdev_is_spacemap_addressable(vdev_t *vd);
extern void vdev_cache_init(vdev_t *vd);
extern void vdev_cache_fini(vdev_t *vd);
extern boolean_t vdev_cache_read(zio_t *zio);
extern void vdev_cache_write(zio_t *zio);
extern void vdev_cache_purge(vdev_t *vd);
extern void vdev_queue_init(vdev_t *vd);
extern void vdev_queue_fini(vdev_t *vd);
extern zio_t *vdev_queue_io(zio_t *zio);