From: Jens Axboe <axboe@kernel.dk>
To: Ming Lei <ming.lei@redhat.com>,
Christoph Hellwig <hch@infradead.org>,
Uday Shankar <ushankar@purestorage.com>
Cc: linux-block@vger.kernel.org, Riley Thomasson <riley@purestorage.com>
Subject: Re: [PATCH v2] ublk: remove segment count and size limits
Date: Tue, 30 Apr 2024 15:37:05 -0600 [thread overview]
Message-ID: <171451302531.24801.16357937130261445082.b4-ty@kernel.dk> (raw)
In-Reply-To: <20240430211623.2802036-1-ushankar@purestorage.com>
On Tue, 30 Apr 2024 15:16:24 -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.
>
> [...]
Applied, thanks!
[1/1] ublk: remove segment count and size limits
commit: eaf4a9b19b9961f8ca294c39c5f8984a4cf42212
Best regards,
--
Jens Axboe
prev parent reply other threads:[~2024-04-30 21:37 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-30 21:16 [PATCH v2] ublk: remove segment count and size limits Uday Shankar
2024-04-30 21:37 ` Jens Axboe [this message]
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