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

在 2026/8/10 11:27, koraynilay 写道:
> On Mon Aug 10, 2026 at 3:54 AM CEST, Qu Wenruo wrote:
>>
>>
>> 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.
> 
> Ah, and in that case, to set compression on the whole fs use btrfs prop to
> set it on the root?

Yep.
> 
>> 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.