btrfs: cleanup metadata page pointer usage

Although we have migrated extent_buffer::pages[] to folios[], we're
still mostly using the folio_page() help to grab the page.

This patch would do the following cleanups for metadata:

- Introduce num_extent_folios() helper
  This is to replace most num_extent_pages() callers.

- Use num_extent_folios() to iterate future large folios
  This allows us to use things like
  bio_add_folio()/bio_add_folio_nofail(), and only set the needed flags
  for the folio (aka the leading/tailing page), which reduces the loop
  iteration to 1 for large folios.

- Change metadata related functions to use folio pointers
  Including their function name, involving:
  * attach_extent_buffer_page()
  * detach_extent_buffer_page()
  * page_range_has_eb()
  * btrfs_release_extent_buffer_pages()
  * btree_clear_page_dirty()
  * btrfs_page_inc_eb_refs()
  * btrfs_page_dec_eb_refs()

- Change btrfs_is_subpage() to accept an address_space pointer
  This is to allow both page->mapping and folio->mapping to be utilized.
  As data is still using the old per-page code, and may keep so for a
  while.

- Special corner case place holder for future order mismatches between
  extent buffer and inode filemap
  For now it's  just a block of comments and a dead ASSERT(), no real
  handling yet.

The subpage code would still go page, just because subpage and large
folio are conflicting conditions, thus we don't need to bother subpage
with higher order folios at all. Just folio_page(folio, 0) would be
enough.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
[ minor styling tweaks ]
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 3 insertions, 5 deletions

diff --git a/fs/btrfs/subpage.h b/fs/btrfs/subpage.h
index 5cbf67ccbdeb..facd5c808e6f 100644
--- a/fs/btrfs/subpage.h
+++ b/fs/btrfs/subpage.h
@@ -73,7 +73,7 @@ enum btrfs_subpage_type {
 	BTRFS_SUBPAGE_DATA,
 };
 
-bool btrfs_is_subpage(const struct btrfs_fs_info *fs_info, struct page *page);
+bool btrfs_is_subpage(const struct btrfs_fs_info *fs_info, struct address_space *mapping);
 
 void btrfs_init_subpage_info(struct btrfs_subpage_info *subpage_info, u32 sectorsize);
 int btrfs_attach_subpage(const struct btrfs_fs_info *fs_info,
@@ -86,10 +86,8 @@ struct btrfs_subpage *btrfs_alloc_subpage(const struct btrfs_fs_info *fs_info,
 					  enum btrfs_subpage_type type);
 void btrfs_free_subpage(struct btrfs_subpage *subpage);
 
-void btrfs_page_inc_eb_refs(const struct btrfs_fs_info *fs_info,
-			    struct page *page);
-void btrfs_page_dec_eb_refs(const struct btrfs_fs_info *fs_info,
-			    struct page *page);
+void btrfs_folio_inc_eb_refs(const struct btrfs_fs_info *fs_info, struct folio *folio);
+void btrfs_folio_dec_eb_refs(const struct btrfs_fs_info *fs_info, struct folio *folio);
 
 void btrfs_subpage_start_reader(const struct btrfs_fs_info *fs_info,
 		struct page *page, u64 start, u32 len);