Hi, With recent folio MM changes, I'm wondering if it's possible to force an address space to always allocate a folio in certain order? E.g. For certain inode, we always allocate pages (folios) in the order of 2 for its page cache. I'm asking this seemingly weird question for the following reasons: - Support multi-page blocksize of various filesystems Currently most file systems only go support sub-page, not multi-page blocksize. Thus if there is forced order for all the address space, it would be much easier to implement multi-page blocksize support. (Although I strongly doubt if we need such multi-page blocksize support for most fses) - For btrfs metadata optimization Btrfs metadata is always using multiple blocks (and power of 2 of cource) for one of its metadata block. Currently we have to do a lot of cross-page handling, if we can ensure all of our metadata block are using folios, we can get rid of such cross-page checks (at a cost of possible higher chance hitting ENOMEM). It looks like our current __filemap_get_folio() is still allocating new folios using fixed order 0, thus it's not really possible for now. Would it be possible in the future or it may need too much work for this to work? (Other than some folio order member in address_space?) Thanks, Qu
