linux-kernel - Re: [PATCH v2 1/2] ublk: use copy_{to,from}

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Message-ID: <aQwinGy55Bk0r-LU@fedora>
Date: Thu, 6 Nov 2025 12:22:52 +0800
From: Ming Lei <ming.lei@...hat.com>
To: Caleb Sander Mateos <csander@...estorage.com>
Cc: Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] ublk: use copy_{to,from}_iter() for user copy

On Wed, Nov 05, 2025 at 01:28:22PM -0700, Caleb Sander Mateos wrote:
> ublk_copy_user_pages()/ublk_copy_io_pages() currently uses
> iov_iter_get_pages2() to extract the pages from the iov_iter and
> memcpy()s between the bvec_iter and the iov_iter's pages one at a time.
> Switch to using copy_to_iter()/copy_from_iter() instead. This avoids the
> user page reference count increments and decrements and needing to split
> the memcpy() at user page boundaries. It also simplifies the code
> considerably.
> Ming reports a 40% throughput improvement when issuing I/O to the
> selftests null ublk server with zero-copy disabled.
> 
> Signed-off-by: Caleb Sander Mateos <csander@...estorage.com>

Reviewed-by: Ming Lei <ming.lei@...hat.com>

Thanks,
Ming