mpage: convert __mpage_writepage() to use a folio more fully

This is just a conversion to the folio API.  While there are some nods
towards supporting multi-page folios in here, the blocks array is still
sized for one page's worth of blocks, and there are other assumptions such
as the blocks_per_page variable.

[[email protected]: fix accidentally-triggering WARN_ON_ONCE]
  Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Matthew Wilcox (Oracle) <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Jan Kara <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
1 file changed