RE: [PATCH v7 0/3] FDP and per-io hints

Javier Gonzalez
2024-10-15T03:08:03Z

> On Mon, Oct 14, 2024 at 09:08:24AM +0000, Javier Gonzalez wrote:
> > > Especially as it directly undermindes any file system work to actually make use
> of it.
> >
> > I do not think it does. If a FS wants to use the temperatures, then they
> > would be able to leverage FDP besides SCSI.
>
> What do you mean with that? This is a bit too much whitepaper vocabularly.
>
> We have code in XFS that can make use of the temperature hint. But to
> make them work it actually needs to do real stream separation on the
> device. I.e. the file system consumes the temperature hints.

The device can guarantee the stream separation without knowing the temperature.

> > And if we come up with a better interface later on, we can make the changes
> then.
> > I really do not see the issue. If we were adding a temperature abstraction now, I
> would agree with
> > You that we would need to cover the use-case you mention for FSs from the
> beginning, but this
> > Is already here. Seems like a fair compromise to support current users.
>
> Again, I think the temperature hints at the syscall level aren't all
> bad. There's definitively a few things I'd like to do better in hindsight,
> but that's not the point. The problem is trying to turn them into
> stream separation all the way down in the driver, which is fundamentally
> broken.
>
> > - How do we convince VFS folks to give us more space for hints at this point?
>
> What space from VFS folks do you need for hints? And why does it
> matter?

We need space in the inode to store the hint ID.

Look, this feels like going in circles. All this gaslighting is what makes it difficult to
push patches when you just do not like the feature. It is the 3rd time I propose you
a way forward and you simply cannot provide any specific technical feedback - in the
past email I posted several questions about the interface you seem to be talking
about and you explicitly omit that.