swap: use bdev_read_page() / bdev_write_page()
swap: use bdev_read_page() / bdev_write_page()

By calling the device driver to write the page directly, we avoid
allocating a BIO, which allows us to free memory without allocating
memory.

[5c1e68b099950c134891f0b6e179498a8ebe9cf9@linux-foundation.org: fix used-uninitialized bug]
Signed-off-by: Matthew Wilcox <ed1245e46949b7b8f2bca25d41520ebc8aeefcf8@intel.com>
Cc: Dave Chinner <aa743a0aaec8f7d7a1f01442503957f4d7a2d634@fromorbit.com>
Cc: Dheeraj Reddy <19757dce1266703088c4d5bd07ae2110854a1de4@intel.com>
Cc: Hugh Dickins <d3abdf3e2800e6cb849f11b81e6eb50b34d96431@google.com>
Signed-off-by: Andrew Morton <5c1e68b099950c134891f0b6e179498a8ebe9cf9@linux-foundation.org>
Signed-off-by: Linus Torvalds <69652caca27c8b940640ad396ab71f93cacec34f@linux-foundation.org>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs