[PATCH v2 2/2] btrfs: remove the trailing zeros from compressed inline extent

[Qu Wenruo <wqu@suse.com>]

[BEHAVIOR CHANGE]
After commit 3eaf5f082c4c ("btrfs: extract inlined creation into a
dedicated delalloc helper"), btrfs changed its behavior when generating
compressed inlined extents.

Previously the compression input was the file range [0, i_size), but
after that commit the input is file range [0, sectorsize).

This means the decompression handling needs to have a buffer that is no
smaller than sectorsize, or the decompression will fail.

This has already caused problems for other projects, like u-boot and
btrfs-restore from btrfs-progs.
Although those projects are fixed with a more robust decompression path,
this kernel change also causes extra space usage for compressed inlined
extents:

 All doing a 3K writes with content filled with 0xcd

 Before:
        item 6 key (257 EXTENT_DATA 0) itemoff 15794 itemsize 69
                generation 9 type 0 (inline)
                inline extent data size 48 ram_bytes 3072 compression 2 (lzo) encryption 0

 After:
         item 6 key (257 EXTENT_DATA 0) itemoff 15781 itemsize 82
                generation 9 type 0 (inline)
                inline extent data size 61 ram_bytes 3072 compression 2 (lzo) encryption 0

This behavior change also increased the lzo compressed size from 48 bytes to 61 bytes.

[FIX]
The previous patch "btrfs: lzo: fix space saving checks which prevents
inline extents" fixed a regression in lzo_compress_bio() where it doesn't
properly handle ranges smaller than a sector.

With that regression fixed, we can finally pass the range [0, i_size) into
btrfs_compress_bio(), and this gets rid of the trailing zeros,
restoring the old behavior, along with the older and better
compression ratio.

Fixes: 3eaf5f082c4c ("btrfs: extract inlined creation into a dedicated delalloc helper")
Reported-by: Hanabishi <i.r.e.c.c.a.k.u.n+kernel.org@gmail.com>
Link: https://lore.kernel.org/linux-btrfs/c97652a5-ac6b-4de6-aa23-3cdebc01d00b@gmail.com/
Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/inode.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 53f4532593b3..5e083ea5c577 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -2342,12 +2342,7 @@ static int run_delalloc_inline(struct btrfs_inode *inode, struct folio *locked_f
 		} else if (inode->prop_compress) {
 			compress_type = inode->prop_compress;
 		}
-		/*
-		 * We need to pass blocksize and not i_size, otherwise we can't
-		 * create compressed inline extents for data smaller than sector
-		 * size with lzo.
-		 */
-		cb = btrfs_compress_bio(inode, 0, blocksize, compress_type, compress_level, 0);
+		cb = btrfs_compress_bio(inode, 0, i_size, compress_type, compress_level, 0);
 		if (IS_ERR(cb)) {
 			cb = NULL;
 			/* Just fall back to non-compressed case. */
-- 
2.55.0