From: Uday Shankar <ushankar@purestorage.com>
To: Ming Lei <ming.lei@redhat.com>, Jens Axboe <axboe@kernel.dk>
Cc: linux-block@vger.kernel.org,
Uday Shankar <ushankar@purestorage.com>,
Riley Thomasson <riley@purestorage.com>
Subject: [PATCH] ublk: remove segment count and size limits
Date: Mon, 29 Apr 2024 18:53:31 -0600 [thread overview]
Message-ID: <20240430005330.2786014-1-ushankar@purestorage.com> (raw)
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>
---
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;
+
if (wait_for_completion_interruptible(&ub->completion) != 0)
return -EINTR;
--
2.34.1
next reply other threads:[~2024-04-30 0:54 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-30 0:53 Uday Shankar [this message]
2024-04-30 9:15 ` [PATCH] ublk: remove segment count and size limits Ming Lei
2024-04-30 12:59 ` Christoph Hellwig
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