[PATCHv10 9/9] scsi: set permanent stream count in block limits

[Hans Holmberg]

On Thu, Oct 31, 2024 at 3:06 PM Keith Busch <kbusch at kernel.org> wrote:
>
> On Thu, Oct 31, 2024 at 09:19:51AM +0100, Hans Holmberg wrote:
> > On Wed, Oct 30, 2024 at 11:33 PM Keith Busch <kbusch at kernel.org> wrote:
> > > That is very much apples-to-oranges. The B+ isn't on the same device
> > > being evaluated for WAF, where this has all that mixed in. I think the
> > > results are pretty good, all things considered.
> >
> > No. The meta data IO is just 0.1% of all writes, so that we use a
> > separate device for that in the benchmark really does not matter.
>
> It's very little spatially, but they overwrite differently than other
> data, creating many small holes in large erase blocks.

I don't really get how this could influence anything significantly.(If at all).

>
> > Since we can achieve a WAF of ~1 for RocksDB on flash, why should we
> > be content with another 67% of unwanted device side writes on top of
> > that?
> >
> > It's of course impossible to compare your benchmark figures and mine
> > directly since we are using different devices, but hey, we definitely
> > have an opportunity here to make significant gains for FDP if we just
> > provide the right kernel interfaces.
> >
> > Why shouldn't we expose the hardware in a way that enables the users
> > to make the most out of it?
>
> Because the people using this want this interface. Stalling for the last
> 6 months hasn't produced anything better, appealing to non-existent
> vaporware to block something ready-to-go that satisfies a need right
> now is just wasting everyone's time.
>
> Again, I absolutely disagree that this locks anyone in to anything.
> That's an overly dramatic excuse.

Locking in or not, to constructively move things forward (if we are
now stuck on how to wire up fs support) I believe it would be
worthwhile to prototype active fdp data placement in xfs and evaluate
it. Happy to help out with that.

Fdp and zns are different beasts, so I don't expect the results in the
presentation to be directly translatable but we can see what we can
do.

Is RocksDB the only file system user at the moment?
Is the benchmark setup/config something that could be shared?