On Tue, Aug 17, 2021 at 05:38:48PM +0800, Qu Wenruo wrote:

Currently we use u16 bitmap to make 4k sectorsize work for 64K page
size.

But this u16 bitmap is not large enough to contain larger page size like
128K, nor is space efficient for 16K page size.

To handle both cases, here we pack all subpage bitmaps into a larger
bitmap, now btrfs_subpage::bitmaps[] will be the ultimate bitmap for
subpage usage.

This is the first step towards more page size support.

Although to really enable extra page size like 16K and 128K, we need to
rework the metadata alignment check.
Which will happen in another patchset.

Changelog:
v2:
- Add two refactor patches to make btrfs_alloc_subpage() more readable
- Fix a break inside two loops bug
- Rename subpage_info::*_start to subpage_info::*_offset
- Add extra comment on what each subpage_info::*_offset works


Qu Wenruo (4):
  btrfs: only call btrfs_alloc_subpage() when sectorsize is smaller than
    PAGE_SIZE
  btrfs: make btrfs_alloc_subpage() to return struct btrfs_subpage *
    directly
  btrfs: introduce btrfs_subpage_bitmap_info
  btrfs: subpage: pack all subpage bitmaps into a larger bitmap

With a few fixups added to misc-next, thanks. I haven't tested it on
subpage config.