Re: apply different compress/compress-force settings on different subvolumes ?

["Chris Murphy" <lists@colorremedies.com>]

On Wed, Feb 21, 2024, at 8:25 PM, Qu Wenruo wrote:

> OK, didn't expect the compression ratio detection to cause so much
> difference.
>
> Which also means, we can further improve the compression detection.
>
> In that case, I would purpose to change "compress-force" to
> "skip_compress_heuristic" or something similar, and get rid of the
> compression string/level for the new option.

But which heuristic is skipped? I assume it can only be the btrfs built-in one? I'm not sure about other compression algorithms but zstandard has its own bail-out heuristic.

Another potentially large difference between compress and compress-force is extent size is limited to 512 KIB even when not compressed using compress-force. Whereas the upper limit on extent size for compress option, is (I think) bg size. An upper limit of 512 KiB on extent size can significantly increase the metadata requirement, leading to tall trees. That then makes me wonder if such setups should have a larger node/leaf size than 16KiB default. 

I'm also not sure which heuristic is cheaper, or more accurate, the built-in Btrfs one or zstandard.


-- 
Chris Murphy