From: Uday Shankar <ushankar@purestorage.com>
To: Ming Lei <ming.lei@redhat.com>, Jens Axboe <axboe@kernel.dk>,
Christoph Hellwig <hch@infradead.org>
Cc: linux-block@vger.kernel.org,
Uday Shankar <ushankar@purestorage.com>,
Riley Thomasson <riley@purestorage.com>
Subject: [PATCH v2] ublk: remove segment count and size limits
Date: Tue, 30 Apr 2024 15:16:24 -0600 [thread overview]
Message-ID: <20240430211623.2802036-1-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>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
---
Changes since v1 (https://lore.kernel.org/linux-block/20240430005330.2786014-1-ushankar@purestorage.com/):
- Moved max_segments and max_segment_size into the designated
initializer
drivers/block/ublk_drv.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
index bea3d5cf8a83..374e4efa8759 100644
--- a/drivers/block/ublk_drv.c
+++ b/drivers/block/ublk_drv.c
@@ -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;
--
2.34.1
next reply other threads:[~2024-04-30 21:21 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-30 21:16 Uday Shankar [this message]
2024-04-30 21:37 ` [PATCH v2] ublk: remove segment count and size limits Jens Axboe
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