Re: dm vdo: add optional Intel IAA-backed compression support

On 5/4/26 12:01 PM, Mikulas Patocka wrote:
> 
> 
> On Wed, 29 Apr 2026, Matthew Sakai wrote:
> 
>>
>>
>> On 4/29/26 11:24 AM, Mikulas Patocka wrote:
>>> Hi
>>>
>>> I think the best way how to support it would be to modify the VDO target
>>> to use the asynchronous compression API (so that it could use arbitrary
>>> algorithms). Then, the support for IAA could be plugged in easily with
>>> little or no extra code.
>>
>> I agree that this is the right approach, but supporting arbitrary compression
>> algorithms will require some significant changes on its own. dm-vdo currently
>> has nowhere to store information about what algorithm is used for which
>> blocks, so it would require reworking the metadata. (We would probably store
> 
> You can store the algorithm in the superblock and use it for all blocks on
> the device. This would be not as flexible as per-block algorithm
> specification, but it should be relatively easy to implement - and it
> would allow you to evaluate whether different algorithms improve
> performance or compression ratio.

We could do that, certainly. It means picking the compression algorithm 
at format time, which also means no existing vdo volumes could take 
advantage of it. But we'd still need an upgrade for existing volumes to 
handle the new superblock field. I think managing the compression 
algorithm per-block is not that much more work, especially since I've 
already written much of it.

>> the extra compression information in the compression block header.) This
>> metadata rework in turn will require some effort to make sure we can continue
>> to support existing users who will want to continue to use dm-vdo volumes in
>> the current format.
> 
> Mikulas
>