Re: [PATCH v2 0/2] btrfs: migrate extent_buffer::pages[] to folio and more cleanups

[David Sterba <dsterba@suse.cz>]

On Fri, Dec 01, 2023 at 04:36:53PM +1030, Qu Wenruo wrote:
> [CHANGELOG]
> v2:
> - Adda new patch to do more cleanups for metadata page pointers usage
> 
> This patchset would migrate extent_buffer::pages[] to folios[], then
> cleanup the existing metadata page pointer usage to proper folios ones.
> 
> This cleanup would help future higher order folios usage for metadata in
> the following aspects:
> 
> - No more need to iterate through the remaining pages for page flags
>   We just call folio_set/mark/start_*() helpers, for the single folio.
>   The helper would only set the flag (mostly for the leading page).
> 
> - Single bio_add_folio() call for the whole eb
> 
> - Better filio helpers naming
>   PageUptodate() compared to folio_test_uptodate().
> 
> The first patch would do a very simple conversion, then the 2nd patch do
> the prepartion for the higher order folio situation.
> 
> There are two locations which won't be converted to folios yet:
> 
> - Subpage code
>   There is no meaning to support higher order folio for subpage.
>   The two conditions are just conflicting with each other.
> 
> - Data page pointers
>   That would be more useful in the future, before we going to support
>   multi-page sectorsize.
> 
> However the 2nd one would also add a new corner case:
> 
> - Order mismatch in filemap and eb folios
>   Unforatunately I don't have a better plan other than re-allocate the
>   folios to the same order.
>   Maybe in the future we would have better ways to handle it? Like
>   migrating the pages to the higher order one?

As long as it's a no-op for now this is OK, we can do the higher order
allocation for eb pages afterwards.