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

在 2026/8/10 10:35, koraynilay 写道:
> On Mon Aug 10, 2026 at 2:51 AM CEST, Qu Wenruo wrote:
>>>>>> So either option 2 or 3 would be fine to me. Although I personally prefer
>>>>>> option 3 a little more, just because it's much cleaner code wise.
>>>>>
>>>>> Option 2 preserves legacy behavior that is 12 years old now, and it
>>>>> costs a single comparison in two 'if' statements.
>>>>>
>>>>> Option 3 makes an already confusing situation worse--it makes the
>>>>> underspecified behavior change depending on kernel version.
>>>>
>>>> One should never rely on something not documented in the first place.
>>>
>>> Option 3 prevents existing mount-option compression level specifications
>>> from working when the attribute agress with the mount option; otherwise,
>>> they would be blocked by a btrfs.compression string that doesn't specify
>>> a level.  That's a _regression_.
>>
>> Let me be this clear, the current one nor option 2 is not working either.
>>
>> If the current algo is different from the XATTR algo, it will be
>> whatever random number clamped to the XATTR algo for the current code.
>>
>> This applies to the option 2 solution. When mount option changed, the
>> level will suddenly change from whatever previous mount option to the
>> default.
> 
> TBF, I can see how it could be useful (or rather, how it could be good
> to have it as an option) to have some files with btrfs.compression="zstd"
> and then use -o compress= to decide on the fly how much compressed the
> new data added to them should be.
> Both are (read: will be, after the per-inode patch) 1 command away, but
> there *might* be use-cases where mount is more suitable.

To be honest, with the proper XATTR compression level specification, I 
think we should even deprecate compress= mount option, and make the 
XATTR one the only recommended way to specific compression.

There are already too many corner cases with mount option.

IMHO, a good design should allow and only allow the best way to do a thing.

And option 3 matches perfect for the XATTR only compression future. It 
still allows old XATTR to work, have a very sane default level, very 
explicit and clear independent from whatever stupid mount option there 
could be.

> 
> 
>>>       https://wiki.tnonline.net/w/Btrfs/Compression
>>
>> The first URL doesn't even resolve here.
> (for some reason it's down right now :(, it was up < 1 hour ago).
> 
> Best,
> koraynilay