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ublk: remove segment count and size limits 

ublk_drv currently creates block devices with the default max_segments
and max_segment_size limits of BLK_MAX_SEGMENTS (128) and
BLK_MAX_SEGMENT_SIZE (65536) respectively. These defaults can
artificially constrain the I/O size seen by the ublk server - for
example, suppose that the ublk server has configured itself to accept
I/Os up to 1M and the application is also issuing 1M sized I/Os. If the
I/O buffer used by the application is backed by 4K pages, the buffer
could consist of up to 1M / 4K = 256 physically discontiguous segments
(even if the buffer is virtually contiguous). As such, the I/O could
exceed the default max_segments limit and get split. This can cause
unnecessary performance issues if the ublk server is optimized to handle
1M I/Os. The block layer's segment count/size limits exist to model
hardware constraints which don't exist in ublk_drv's case, so just
remove those limits for the block devices created by ublk_drv.

Signed-off-by: Uday Shankar <ushankar@purestorage.com>
Reviewed-by: Riley Thomasson <riley@purestorage.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20240430211623.2802036-1-ushankar@purestorage.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Uday Shankar 2024-04-30 15:16:24 -06:00 committed by Jens Axboe
parent 01bc4fda9e
commit eaf4a9b19b
1 changed files with 2 additions and 1 deletions
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3
drivers/block/ublk_drv.c
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@ -2177,7 +2177,8 @@ static int ublk_ctrl_start_dev(struct ublk_device *ub, struct io_uring_cmd *cmd)
.max_hw_sectors = p->max_sectors,
.chunk_sectors = p->chunk_sectors,
.virt_boundary_mask = p->virt_boundary_mask,
.max_segments = USHRT_MAX,
.max_segment_size = UINT_MAX,
};
struct gendisk *disk;
int ret = -EINVAL;