Page I/O

This patch set implements pageio as I described in my talk at
Linux.Conf.AU.  It's for review more than application, I think
benchmarking is going to be required to see if it's a win.  We've done
some benchmarking with an earlier version of the patch and a Chatham card,
and it's a win for us.

The fundamental point of these patches is that we *can* do I/O without
allocating a BIO (or request, or ...) and so we can end up doing fun
things like swapping out a page without allocating any memory.

Possibly it would be interesting to do sub-page I/Os (ie change the
rw_page prototype to take a 'start' and 'length' instead of requiring the
I/O to be the entire page), but the problem then arises about what the
'done' callback should be.

Keith Busch (1):
  NVMe: Add support for rw_page

Matthew Wilcox (5):
  Add bdev_read_page() and bdev_write_page()
  Factor page_endio() out of mpage_end_io()
  swap: Use bdev_read_page() / bdev_write_page()
  brd: Add support for rw_page
  virtio_blk: Add rw_page implementation

 drivers/block/brd.c        |   10 +++
 drivers/block/nvme-core.c  |  129 ++++++++++++++++++++++++++++++++++++---------
 drivers/block/virtio_blk.c |   44 +++++++++++++++
 fs/block_dev.c             |   34 +++++++++++
 fs/mpage.c                 |   83 +++++++++++++++-------------
 include/linux/blkdev.h     |    4 +
 include/linux/pagemap.h    |    2 
 mm/filemap.c               |   25 ++++++++
 mm/page_io.c               |   23 +++++++-
 9 files changed, 288 insertions(+), 66 deletions(-)

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