btrfs: convert submit_eb_subpage() to take a folio

The old page API is being gradually replaced and converted to use folio
to improve code readability and avoid repeated conversion between page
and folio. Moreover, use folio_pos() instead of page_offset(),
which is more consistent with folio usage.
Signed-off-by: Li Zetao <lizetao1@huawei.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent_io.c

@@ -1735,12 +1735,11 @@ static noinline_for_stack void write_one_eb(struct extent_buffer *eb,
  * Return >=0 for the number of submitted extent buffers.
  * Return <0 for fatal error.
  */
-static int submit_eb_subpage(struct page *page, struct writeback_control *wbc)
+static int submit_eb_subpage(struct folio *folio, struct writeback_control *wbc)
 {
-	struct btrfs_fs_info *fs_info = page_to_fs_info(page);
-	struct folio *folio = page_folio(page);
+	struct btrfs_fs_info *fs_info = folio_to_fs_info(folio);
 	int submitted = 0;
-	u64 page_start = page_offset(page);
+	u64 folio_start = folio_pos(folio);
 	int bit_start = 0;
 	int sectors_per_node = fs_info->nodesize >> fs_info->sectorsize_bits;
 
@@ -1755,21 +1754,21 @@ static int submit_eb_subpage(struct page *page, struct writeback_control *wbc)
 		 * Take private lock to ensure the subpage won't be detached
 		 * in the meantime.
 		 */
-		spin_lock(&page->mapping->i_private_lock);
+		spin_lock(&folio->mapping->i_private_lock);
 		if (!folio_test_private(folio)) {
-			spin_unlock(&page->mapping->i_private_lock);
+			spin_unlock(&folio->mapping->i_private_lock);
 			break;
 		}
 		spin_lock_irqsave(&subpage->lock, flags);
 		if (!test_bit(bit_start + btrfs_bitmap_nr_dirty * fs_info->sectors_per_page,
 			      subpage->bitmaps)) {
 			spin_unlock_irqrestore(&subpage->lock, flags);
-			spin_unlock(&page->mapping->i_private_lock);
+			spin_unlock(&folio->mapping->i_private_lock);
 			bit_start++;
 			continue;
 		}
 
-		start = page_start + bit_start * fs_info->sectorsize;
+		start = folio_start + bit_start * fs_info->sectorsize;
 		bit_start += sectors_per_node;
 
 		/*
@@ -1778,7 +1777,7 @@ static int submit_eb_subpage(struct page *page, struct writeback_control *wbc)
 		 */
 		eb = find_extent_buffer_nolock(fs_info, start);
 		spin_unlock_irqrestore(&subpage->lock, flags);
-		spin_unlock(&page->mapping->i_private_lock);
+		spin_unlock(&folio->mapping->i_private_lock);
 
 		/*
 		 * The eb has already reached 0 refs thus find_extent_buffer()
@@ -1829,7 +1828,7 @@ static int submit_eb_page(struct page *page, struct btrfs_eb_write_context *ctx)
 		return 0;
 
 	if (page_to_fs_info(page)->nodesize < PAGE_SIZE)
-		return submit_eb_subpage(page, wbc);
+		return submit_eb_subpage(folio, wbc);
 
 	spin_lock(&mapping->i_private_lock);
 	if (!folio_test_private(folio)) {