btrfs: get rid of compressed_bio::compressed_folios[]

Now there is no one utilizing that member, we can safely remove it along
with compressed_bio::nr_folios member. The size is reduced from 352 to
336 bytes on x86_64.

Reviewed-by: Boris Burkov <boris@bur.io>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Author: adam900710

fs/btrfs/compression.c

@@ -300,7 +300,6 @@ static void end_bbio_compressed_write(struct btrfs_bio *bbio)
 	/* Note, our inode could be gone now. */
 	bio_for_each_folio_all(fi, &bbio->bio)
 		btrfs_free_compr_folio(fi.folio);
-	kfree(cb->compressed_folios);
 	bio_put(&cb->bbio.bio);
 }
 

fs/btrfs/compression.h

@@ -42,12 +42,6 @@ static_assert((BTRFS_MAX_COMPRESSED % PAGE_SIZE) == 0);
 #define	BTRFS_ZLIB_DEFAULT_LEVEL		3
 
 struct compressed_bio {
-	/* Number of compressed folios in the array. */
-	unsigned int nr_folios;
-
-	/* The folios with the compressed data on them. */
-	struct folio **compressed_folios;
-
 	/* starting offset in the inode for our pages */
 	u64 start;