nilfs2: convert segment buffer to be folio-based

nilfs2: convert segment buffer to be folio-based

Patch series "nilfs2: Finish folio conversion".

This series converts all remaining page structure references in nilfs2 to
folio-based, except for nilfs_copy_buffer function, which was converted to
use folios in advance for cross-fs page flags cleanup.

This prioritizes folio conversion, and does not include buffer head
reference reduction, nor does it support for block sizes larger than the
system page size.

The first eight patches in this series mainly convert each of the
nilfs2-specific metadata implementations to use folios.  The last four
patches, by Matthew Wilcox, eliminate aops writepage callbacks and convert
the remaining page structure references to folio-based.  This part
reflects some corrections to the patch series posted by Matthew.

This patch (of 12):

In the segment buffer (log buffer) implementation, two parts of the block
buffer, CRC calculation and bio preparation, are still page-based, so
convert them to folio-based.

Link: https://lkml.kernel.org/r/20241024092602.13395-1-konishi.ryusuke@gmail.com
Link: https://lkml.kernel.org/r/20241024092602.13395-2-konishi.ryusuke@gmail.com
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>