Re: dm kcopyd: Increase sub-job size to 512KiB

[Mike Snitzer <snitzer@redhat.com>]

On Fri, Jul 12 2019 at  9:45am -0400,
Nikos Tsironis <ntsironis@arrikto.com> wrote:

> Hi Mike,
> 
> A kind reminder about this patch. Do you require any changes or will you
> merge it as is?

I think we need changes to expose knob(s) to tune this value on a global
_and_ device level via sysfs.  E.g.:

1) dm_mod module param for global
2) but also allow a per-device override, like:
   echo 512 > /sys/block/dm-X/dm/kcopyd_subjob_size

1 is super easy and is a start.  Layering in 2 is a bit more involved.

In hindsight (given how risk-averse I am on changing the default) I
should've kept the default 128 but allowed override with modparam
dm_mod.kcopyd_subjob_size=1024

Would this be an OK first step?

If so, we're still in the 5.3 merge window, I'll see what I can do.

Thanks,
Mike