linux-kernel - [PATCH v2 0/2] ublk: simplify user copy

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Message-ID: <20251105202823.2198194-1-csander@purestorage.com>
Date: Wed,  5 Nov 2025 13:28:21 -0700
From: Caleb Sander Mateos <csander@...estorage.com>
To: Ming Lei <ming.lei@...hat.com>,
	Jens Axboe <axboe@...nel.dk>
Cc: linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Caleb Sander Mateos <csander@...estorage.com>
Subject: [PATCH v2 0/2] ublk: simplify user copy

Use copy_page_{to,from}_user() and rq_for_each_bvec() to simplify the
implementation of ublk_copy_user_pages(). Avoiding the page pinning and
unpinning saves expensive atomic increments and decrements of the page
reference counts. And copying via user virtual addresses avoids needing
to split the copy at user page boundaries. Ming reports a 40% throughput
improvement when issuing I/O to the selftests null ublk server with
zero-copy disabled.

v2:
- Use rq_for_each_bvec() to further simplify the code (Ming)
- Add performance measurements from Ming

Caleb Sander Mateos (2):
  ublk: use copy_{to,from}_iter() for user copy
  ublk: use rq_for_each_bvec() for user copy

 drivers/block/ublk_drv.c | 113 ++++++++-------------------------------
 1 file changed, 23 insertions(+), 90 deletions(-)

-- 
2.45.2