btrfs: fix the inline compressed extent check in inode_need_compress()

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[BUG]
Since commit 59615e2c1f ("btrfs: reject single block sized compression
early"), the following script will result the inode to have NOCOMPRESS
flag, meanwhile old kernels don't:

  # mkfs.btrfs -f $dev
  # mount $dev $mnt -o max_inline=2k,compress=zstd
  # truncate -s 8k $mnt/foobar
  # xfs_io -f -c "pwrite 0 2k" $mnt/foobar
  # sync

Before that commit, the inode will not have NOCOMPRESS flag:

	item 4 key (257 INODE_ITEM 0) itemoff 15879 itemsize 160
		generation 9 transid 9 size 8192 nbytes 4096
		block group 0 mode 100644 links 1 uid 0 gid 0 rdev 0
		sequence 3 flags 0x0(none)

But after that commit, the inode will have NOCOMPRESS flag:

	item 4 key (257 INODE_ITEM 0) itemoff 15879 itemsize 160
		generation 9 transid 10 size 8192 nbytes 4096
		block group 0 mode 100644 links 1 uid 0 gid 0 rdev 0
		sequence 3 flags 0x8(NOCOMPRESS)

This will make a lot of files no longer to be compressed.

[CAUSE]
The old compressed inline check looks like this:

	if (total_compressed <= blocksize &&
	   (start > 0 || end + 1 < inode->disk_i_size))
		goto cleanup_and_bail_uncompressed;

That inline part check is equal to "!(start == 0 && end + 1 >=
inode->disk_i_size)", but the new check no longer has that disk_i_size
check.

Thus it means any single block sized write at file offset 0 will pass
the inline check, which is wrong.

Furthermore, since we have merged the old check into
inode_need_compress(), there is no disk_i_size based inline check
anymore, we will always try compressing that single block at file offset
0, then later find out it's not a net win and go to the
mark_incompressible tag.

This results the inode to have NOCOMPRESS flag.

[FIX]
Add back the missing disk_i_size based check into inode_need_compress().

Now the same script will no longer cause NOCOMPRESS flag.

Fixes: 59615e2c1f ("btrfs: reject single block sized compression early")
Reported-by: Chris Mason <clm@meta.com>
Link: https://lore.kernel.org/linux-btrfs/20260208183840.975975-1-clm@meta.com/
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

...

This commit is contained in:

Qu Wenruo 2026-02-09 10:51:09 +10:30 • committed by David Sterba

parent 1f3f98e42d

commit 883adb6dcf

1 changed files with 2 additions and 1 deletions

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fs/btrfs/inode.c

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