On Mon, Apr 29, 2024 at 06:53:31PM -0600, Uday Shankar wrote: > 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@xxxxxxxxxxxxxxx> > Reviewed-by: Riley Thomasson <riley@xxxxxxxxxxxxxxx> > --- > drivers/block/ublk_drv.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c > index bea3d5cf8a83..835b0cc7c032 100644 > --- a/drivers/block/ublk_drv.c > +++ b/drivers/block/ublk_drv.c > @@ -2209,6 +2209,9 @@ static int ublk_ctrl_start_dev(struct ublk_device *ub, struct io_uring_cmd *cmd) > lim.max_zone_append_sectors = p->max_zone_append_sectors; > } > > + lim.max_segments = USHRT_MAX; > + lim.max_segment_size = UINT_MAX; Reviewed-by: Ming Lei <ming.lei@xxxxxxxxxx> Thanks, Ming
