mpage: stop using bdev_{read,write}_page

mpage: stop using bdev_{read,write}_page

Patch series "remove ->rw_page".

This series removes the ->rw_page block_device_operation, which is an old
and clumsy attempt at a simple read/write fast path for the block layer.
It isn't actually used by the fastest block layer operations that we
support (polled I/O through io_uring), but only used by the mpage buffered
I/O helpers which are some of the slowest I/O we have and do not make any
difference there at all, and zram which is a block device abused to
duplicate the zram functionality.

Given that zram is heavily used we need to make sure there is a good
replacement for synchronous I/O, so this series adds a new flag for
drivers that complete I/O synchronously and uses that flag to use on-stack
bios and synchronous submission for them in the swap code.

This patch (of 7):

These are micro-optimizations for synchronous I/O, which do not matter
compared to all the other inefficiencies in the legacy buffer_head based
mpage code.

Link: https://lkml.kernel.org/r/20230125133436.447864-1-hch@lst.de
Link: https://lkml.kernel.org/r/20230125133436.447864-2-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Cc: Keith Busch <kbusch@kernel.org>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>