[PATCH RFC 0/2] btrfs: defrag: further preparation for multi-page sector size

[Qu Wenruo <wqu@suse.com>]

With the folio interface, it's much easier to support multi-page sector
size (aka, sector/block size > PAGE_SIZE, which is rare between major
upstream filesystems).

The basic idea is, if we firstly convert to full folio interface, and
allow an address space to only allocate folio which is exactly
block/sector size, the support for multi-page would be mostly done.

But before that support, there are still quite some conversion left for
btrfs.

Furthermore, with both subpage and multipage sector size, we need to
handle folio different:

- For subpage
  The folio would always be page sized.

- For multipage (and regular sectorsize == PAGE_SIZE)
  The folio would be sector sized.

Furthermore, the filemap interface would make various shifts more
complex.
As filemap_*() interfaces use index which is PAGE_SHIFT based,
meanwhile with potential larger folio, the folio shift can be larger
than PAGE_SHIFT.

Thus in the future, we may want to change filemap interface to accept
bytenr to avoid confusion between page and folio shifts.

The first patch would introduce a cached folio size and shift.

The second patch would make defrag to utilize the new cached folio size
and shift.
(And still use PAGE_SHIFT only for filemap*() interfaces)

Qu Wenruo (2):
  btrfs: introduce cached folio size
  btrfs: defrag: prepare defrag for larger data folio size

 fs/btrfs/defrag.c  | 69 +++++++++++++++++++++++++---------------------
 fs/btrfs/disk-io.c | 11 ++++++++
 fs/btrfs/fs.h      | 10 +++++++
 3 files changed, 58 insertions(+), 32 deletions(-)

-- 
2.43.0