On Sat, Jan 16, 2021 at 03:15:18PM +0800, Qu Wenruo wrote:

For btrfs subpage support, we need a structure to record extra info for
the status of each sectors of a page.

This patch will introduce the skeleton structure for future btrfs
subpage support.
All subpage related code would go to subpage.[ch] to avoid populating
the existing code base.

Ok, and after reading more of the patchset it makes even more sense,
handling all the special cases is suitable for a separate file.