Re: [PATCH] btrfs: defrag: add under utilized extent to defrag target list

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

On 2024/1/10 08:27, Christoph Anton Mitterer wrote:
> On Wed, 2024-01-10 at 07:34 +1030, Qu Wenruo wrote:
>> The 1/16 is chosen as a trade-off between wasted space and possible
>> unnecessary defrag.
>
> Felipe's point doesn't seem so invalid.... wouldn't it be possible to
> make the trade-off somehow configurable, so that the user can choose
> via some command line option?

We have 16 bytes extra space for the ioctl, I think we can go 2 u32 to
configure both ratio and wasted space if needed.

Unfortunately we don't have any existing checks on
btrfs_ioctl_defrag_range_args::flags, which means we have no way to
detect if the kernel supports new flags.

I'll start adding such rejection first, then we can start adding new
btrfs_ioctl_defrag_range_args flags/options to support configurable
ratio/wasted bytes.

Thanks,
Qu

>
> Cheers,
> Chris.