vdev_disk: disable flushes if device does not support it
If the underlying device doesn't have a write-back cache, the kernel will just return a successful response. This doesn't hurt anything, but it's extra work on the IO taskqs that are unnecessary. So, detect this when we open the device for the first time. Sponsored-by: Klara, Inc. Sponsored-by: Wasabi Technology, Inc. Reviewed-by: Alexander Motin <mav@FreeBSD.org> Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: Rob Norris <rob.norris@klarasystems.com> Closes #16148
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@ -94,6 +94,33 @@ blk_queue_set_write_cache(struct request_queue *q, bool wc, bool fua)
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#endif
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}
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/*
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* Detect if a device has a write cache. Used to set the intial value for the
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* vdev nowritecache flag.
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*
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* 4.10: QUEUE_FLAG_WC added. Initialised by the driver, but can be changed
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* later by the operator. If not set, kernel will return flush requests
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* immediately without doing anything.
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* 6.6: QUEUE_FLAG_HW_WC added. Initialised by the driver, can't be changed.
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* Only controls if the operator is allowed to change _WC. Initial version
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* buggy; aliased to QUEUE_FLAG_FUA, so unuseable.
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* 6.6.10, 6.7: QUEUE_FLAG_HW_WC fixed.
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*
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* Older than 4.10 we just assume write cache, and let the normal flush fail
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* detection apply.
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*/
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static inline boolean_t
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zfs_bdev_has_write_cache(struct block_device *bdev)
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{
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#if defined(QUEUE_FLAG_HW_WC) && QUEUE_FLAG_HW_WC != QUEUE_FLAG_FUA
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return (test_bit(QUEUE_FLAG_HW_WC, &bdev_get_queue(bdev)->queue_flags));
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#elif defined(QUEUE_FLAG_WC)
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return (test_bit(QUEUE_FLAG_WC, &bdev_get_queue(bdev)->queue_flags));
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#else
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return (B_TRUE);
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#endif
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}
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static inline void
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blk_queue_set_read_ahead(struct request_queue *q, unsigned long ra_pages)
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{
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@ -429,8 +429,11 @@ vdev_disk_open(vdev_t *v, uint64_t *psize, uint64_t *max_psize,
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/* Determine the logical block size */
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int logical_block_size = bdev_logical_block_size(bdev);
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/* Clear the nowritecache bit, causes vdev_reopen() to try again. */
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v->vdev_nowritecache = B_FALSE;
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/*
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* If the device has a write cache, clear the nowritecache flag,
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* so that we start issuing flush requests again.
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*/
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v->vdev_nowritecache = !zfs_bdev_has_write_cache(bdev);
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/* Set when device reports it supports TRIM. */
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v->vdev_has_trim = bdev_discard_supported(bdev);
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