Re: [PATCH 1/2] mkfs: Break block discard into chunks of 2 GB

Pavel Reichl
2019-11-22T16:09:20Z

On Fri, Nov 22, 2019 at 12:18 AM Dave Chinner <david@fromorbit.com> wrote:
>
> On Thu, Nov 21, 2019 at 10:44:44PM +0100, Pavel Reichl wrote:
> > Signed-off-by: Pavel Reichl <preichl@redhat.com>
> > ---
>
> This is mixing an explanation about why the change is being made
> and what was considered when making decisions about the change.

Thanks, I'll try to improve that.
>
> e.g. my first questions on looking at the patch were:
>
> - why do we need to break up the discards into 2GB chunks?
> - why 2GB?
> - why not use libblkid to query the maximum discard size
> and use that as the step size instead?

This is new for me, please let me learn more about that.

> - is there any performance impact from breaking up large
> discards that might be optimised by the kernel into many
> overlapping async operations into small, synchronous
> discards?

Honestly, I don't have an answer for that ATM - it's quite possible.
It certainly needs more investigating. On the other hand - current
lack of feedback causes user discomfort. So I'd like to know your
opinion - should the change proposed by this patch be default
behaviour (as it may be more user friendly) and should we add an
option that would 'revert' to current behaviour (that would be for
informed user).

>
> i.e. the reviewer can read what the patch does, but that deosn't
> explain why the patch does this. Hence it's a good idea to explain
> the problem being solved or the feature requirements that have lead
> to the changes in the patch....
>
> Cheers,
>
> Dave.
> --
> Dave Chinner
> david@fromorbit.com
>