Re: [PATCH 00/12] btrfs: remap tree

[Mark Harmstone <maharmstone@meta.com>]

On 9/6/25 19:51, David Sterba wrote:
> > 
> On Thu, Jun 05, 2025 at 05:23:30PM +0100, Mark Harmstone wrote:
>> * The remap tree doesn't have metadata items in the extent tree (thanks to Josef
>>    for the suggestion). This was to work around some corruption that delayed refs
>>    were causing, but it also fits it with our future plans of removing all
>>    metadata items for COW-only trees, reducing write amplification.
> 
>>    A knock-on effect of this is that I've had to disable balancing of the remap
>>    chunk itself.
> 
> Not relocatable at all? How will the shrink or device deletion work,
> this uses relocation to move the chunks.

I know, it won't. At the moment this is more-or-less limited to 
single-volume devices that you don't shrink.

This is something I'm going to address with a future patch before this 
leaves experimental. It won't require any more format changes, it's just 
that this bit is tricky to get right.

> 
>>    This is because we can no longer walk the extent tree, and will
>>    have to walk the remap tree instead. When we remove the COW-only metadata
>>    items, we will also have to do this for the chunk and root trees, as
>>    bootstrapping means they can't be remapped.