Re: [PATCH 0/4] btrfs: add per-inode compression levels in xattrs

["koraynilay" <koray.fra@gmail.com>]

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On Sun Aug 9, 2026 at 2:17 AM CEST, Qu Wenruo wrote:
> I'm not sure if this is the correct behavior in the first place.
>
> As you already mentioned, zstd and zlib have very different compression 
> level range, using the incorrect level makes no sense (and it's being 
> clamped anyway).
>
> I think we should go the default level when not specified, which makes 
> more sense, and that would definitely be something worth fixing.

Yes, I also think that would be best, but my main concern would be it
changing how chattr +c behaves (I'm less concerned about the btrfs prop
set file compression "zstd" case, since IMO that implies the user wants
the default level).

The options I considered were:
1) keep the "bug", like I did for now;
2) keep the "bug", but only if the compress= algo is the same
   as the btrfs.compression one, if they aren't, use the default for the
   btrfs.compression algo (e.g. compress=zstd:15 and btrfs.compression=zlib
   would compress the extent at zlib:3 instead of clamp(zlib, 15) = 9)
   (suggested by Zygo);
3) fix the "bug" entirely, which is what I actually accidentally did at
   first, by just setting compress_level = inode->prop_compress_level
   without any check prior to that (which means that by default it would
   use algo:0).

Option 2) is probably the best compromise between breaking existing
scripts and the behaviour making sense, plus it shouldn't change the
chattr +c behaviour, since btrfs takes the algorithm from compress=.

Thanks.

Best,
koraynilay

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