[dm-devel] dm kcopyd: Increase sub-job size to 512KiB

[Nikos Tsironis]

On 7/15/19 9:22 PM, Mike Snitzer wrote:
> On Fri, Jul 12 2019 at  9:45am -0400,
> Nikos Tsironis <ntsironis at 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
> 

Hi Mike,

Thanks for your feedback. I agree, this sounds like the best thing to do.

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

Maybe I could help with (2). We could discuss about it and how you think
it's best to do it and then I could proceed with an implementation.

Please let me know what you think.

> 
> 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?

Yes, this would be great.

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

Shall I proceed with a patch adding the dm_mod.kcopyd_subjob_size
modparam?

Thanks,
Nikos

> 
> Thanks,
> Mike
>