[PATCH net-next V4 0/5] vhost: accelerate metadata access through vmap()

[Jason Wang <jasowang@redhat.com>]

This series tries to access virtqueue metadata through kernel virtual
address instead of copy_user() friends since they had too much
overheads like checks, spec barriers or even hardware feature
toggling.

Test shows about 24% improvement on TX PPS. It should benefit other
cases as well.

Changes from V3:
- don't try to use vmap for file backed pages
- rebase to master
Changes from V2:
- fix buggy range overlapping check
- tear down MMU notifier during vhost ioctl to make sure invalidation
  request can read metadata userspace address and vq size without
  holding vq mutex.
Changes from V1:
- instead of pinning pages, use MMU notifier to invalidate vmaps and
  remap duing metadata prefetch
- fix build warning on MIPS

Jason Wang (5):
  vhost: generalize adding used elem
  vhost: fine grain userspace memory accessors
  vhost: rename vq_iotlb_prefetch() to vq_meta_prefetch()
  vhost: introduce helpers to get the size of metadata area
  vhost: access vq metadata through kernel virtual address

 drivers/vhost/net.c   |   4 +-
 drivers/vhost/vhost.c | 441 +++++++++++++++++++++++++++++++++++++-----
 drivers/vhost/vhost.h |  15 +-
 mm/shmem.c            |   1 +
 4 files changed, 410 insertions(+), 51 deletions(-)

-- 
2.17.1