[LSF/MM/BPF TOPIC] : Flexible Data Placement (FDP) availability for kernel space file systems

[Javier González]

On 15.01.2024 11:46, Viacheslav Dubeyko wrote:
>Hi Javier,
>
>Samsung introduced Flexible Data Placement (FDP) technology
>pretty recently. As far as I know, currently, this technology
>is available for user-space solutions only. I assume it will be
>good to have discussion how kernel-space file systems could
>work with SSDs that support FDP technology by employing
>FDP benefits.

Slava,

Thanks for bringing this up.

First, this is not a Samsung technology. Several vendors are building
FDP and several customers are already deploying first product.

We enabled FDP thtough I/O Passthru to avoid unnecesary noise in the
block layer until we had a clear idea on use-cases. We have been
following and reviewing Bart's write hint series and it covers all the
block layer and interface needed to support FDP. Currently, we have
patches with small changes to wire the NVMe driver. We plan to submit
them after Bart's patches are applied. Now it is a good time since we
have LSF and there are also 2 customers using FDP on block and file.

>
>How soon FDP API will be available for kernel-space file systems?

The work is done. We will submit as Bart's patches are applied.

Kanchan is doing this work.

>How kernel-space file systems can adopt FDP technology?

It is based on write hints. There is no FS-specific placement decisions.
All the responsibility is in the application.

Kanchan: Can you comment a bit more on this?

>How FDP technology can improve efficiency and reliability of
>kernel-space file system?

This is an open problem. Our experience is that making data placement
decisions on the FS is tricky (beyond the obvious data / medatadata). If
someone has a good use-case for this, I think it is worth exploring.
F2FS is a good candidate, but I am not sure FDP is of interest for
mobile - here ZUFS seems to be the current dominant technology.

>Which new challenges FDP technology introduces for kernel-space
>file systems?

See above. All we have done is wire up the NVMe driver. This is a good
discussion for LSF/

>Could we have such discussion leading from Samsung side?

Of course. We are happy to host a session on this if it gets selected.
We will add it to one of our submission.