Re: [PATCH v2 8/8] bdev: use bdev_io_min() for statx block size

Hannes Reinecke
2025-02-05T16:22:49Z

On 2/5/25 00:12, Luis Chamberlain wrote:
> You can use lsblk to query for a block device block device block size:
>
> lsblk -o MIN-IO /dev/nvme0n1
> MIN-IO
> 4096
>
> The min-io is the minimum IO the block device prefers for optimal
> performance. In turn we map this to the block device block size.
> The current block size exposed even for block devices with an
> LBA format of 16k is 4k. Likewise devices which support 4k LBA format
> but have a larger Indirection Unit of 16k have an exposed block size
> of 4k.
>
> This incurs read-modify-writes on direct IO against devices with a
> min-io larger than the page size. To fix this, use the block device
> min io, which is the minimal optimal IO the device prefers.
>
> With this we now get:
>
> lsblk -o MIN-IO /dev/nvme0n1
> MIN-IO
> 16384
>
> And so userspace gets the appropriate information it needs for optimal
> performance. This is verified with blkalgn against mkfs against a
> device with LBA format of 4k but an NPWG of 16k (min io size)
>
> mkfs.xfs -f -b size=16k /dev/nvme3n1
> blkalgn -d nvme3n1 --ops Write
>
> Block size : count distribution
> 0 -> 1 : 0 | |
> 2 -> 3 : 0 | |
> 4 -> 7 : 0 | |
> 8 -> 15 : 0 | |
> 16 -> 31 : 0 | |
> 32 -> 63 : 0 | |
> 64 -> 127 : 0 | |
> 128 -> 255 : 0 | |
> 256 -> 511 : 0 | |
> 512 -> 1023 : 0 | |
> 1024 -> 2047 : 0 | |
> 2048 -> 4095 : 0 | |
> 4096 -> 8191 : 0 | |
> 8192 -> 16383 : 0 | |
> 16384 -> 32767 : 66 |****************************************|
> 32768 -> 65535 : 0 | |
> 65536 -> 131071 : 0 | |
> 131072 -> 262143 : 2 |* |
> Block size: 14 - 66
> Block size: 17 - 2
>
> Algn size : count distribution
> 0 -> 1 : 0 | |
> 2 -> 3 : 0 | |
> 4 -> 7 : 0 | |
> 8 -> 15 : 0 | |
> 16 -> 31 : 0 | |
> 32 -> 63 : 0 | |
> 64 -> 127 : 0 | |
> 128 -> 255 : 0 | |
> 256 -> 511 : 0 | |
> 512 -> 1023 : 0 | |
> 1024 -> 2047 : 0 | |
> 2048 -> 4095 : 0 | |
> 4096 -> 8191 : 0 | |
> 8192 -> 16383 : 0 | |
> 16384 -> 32767 : 66 |****************************************|
> 32768 -> 65535 : 0 | |
> 65536 -> 131071 : 0 | |
> 131072 -> 262143 : 2 |* |
> Algn size: 14 - 66
> Algn size: 17 - 2
>
> Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
> ---
> block/bdev.c | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
--
Dr. Hannes Reinecke Kernel Storage Architect
hare@suse.de +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
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