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vdev_disk: disable flushes if device does not support it

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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
This commit is contained in:
Rob N
2024-05-03 08:18:35 +10:00
committed by GitHub
parent 645b833079
commit 8f1b7a6fa6
2 changed files with 32 additions and 2 deletions
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include/os/linux/kernel/linux/blkdev_compat.h
+27
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@@ -94,6 +94,33 @@ blk_queue_set_write_cache(struct request_queue *q, bool wc, bool fua)
#endif
}
/*
* Detect if a device has a write cache. Used to set the intial value for the
* vdev nowritecache flag.
*
* 4.10: QUEUE_FLAG_WC added. Initialised by the driver, but can be changed
* later by the operator. If not set, kernel will return flush requests
* immediately without doing anything.
* 6.6: QUEUE_FLAG_HW_WC added. Initialised by the driver, can't be changed.
* Only controls if the operator is allowed to change _WC. Initial version
* buggy; aliased to QUEUE_FLAG_FUA, so unuseable.
* 6.6.10, 6.7: QUEUE_FLAG_HW_WC fixed.
*
* Older than 4.10 we just assume write cache, and let the normal flush fail
* detection apply.
*/
static inline boolean_t
zfs_bdev_has_write_cache(struct block_device *bdev)
{
#if defined(QUEUE_FLAG_HW_WC) && QUEUE_FLAG_HW_WC != QUEUE_FLAG_FUA
return (test_bit(QUEUE_FLAG_HW_WC, &bdev_get_queue(bdev)->queue_flags));
#elif defined(QUEUE_FLAG_WC)
return (test_bit(QUEUE_FLAG_WC, &bdev_get_queue(bdev)->queue_flags));
#else
return (B_TRUE);
#endif
}
static inline void
blk_queue_set_read_ahead(struct request_queue *q, unsigned long ra_pages)
{