[PATCH v3 0/2] ublk: simplify user copy

[Caleb Sander Mateos <csander@purestorage.com>]

Use copy_page_{to,from}_user() and rq_for_each_segment() 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.

v3:
- Use rq_for_each_segment() to avoid copying multi-page bvecs (Ming)
- Add Reviewed-by from Ming

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_segment() for user copy

 drivers/block/ublk_drv.c | 114 +++++++++------------------------------
 1 file changed, 24 insertions(+), 90 deletions(-)

-- 
2.45.2