Re: [PATCH v3] Weighted interleave auto-tuning

[Honggyu Kim]

Hi Ying,

On 1/22/2025 10:24 AM, Huang, Ying wrote:

[snip]

> > > > diff --git a/Documentation/ABI/testing/sysfs-kernel-mm-mempolicy-weighted-interleave b/Documentation/ABI/testing/sysfs-kernel-mm-mempolicy-weighted-interleave
> > > > index 0b7972de04e9..d30dc29c53ff 100644
> > > > --- a/Documentation/ABI/testing/sysfs-kernel-mm-mempolicy-weighted-interleave
> > > > +++ b/Documentation/ABI/testing/sysfs-kernel-mm-mempolicy-weighted-interleave
> > > > @@ -20,6 +20,30 @@ Description:	Weight configuration interface for nodeN
> > > >    		Minimum weight: 1
> > > >    		Maximum weight: 255
> > > >    -		Writing an empty string or `0` will reset the weight
> > > > to the
> > > > -		system default. The system default may be set by the kernel
> > > > -		or drivers at boot or during hotplug events.
> > > > +		Writing invalid values (i.e. any values not in [1,255],
> > > > +		empty string, ...) will return -EINVAL.
> > > > +
> > > > +What:		/sys/kernel/mm/mempolicy/weighted_interleave/mode
> > > > +Date:		January 2025
> > > > +Contact:	Linux memory management mailing list <linux-mm@xxxxxxxxx>
> > > > +Description:	Auto-weighting configuration interface
> > > > +
> > > > +		Configuration modes for weighted interleave. Can take one of
> > > > +		two options: "manual" and "auto". Default is "auto".
> > > > +
> > > > +		In auto mode, all node weights are re-calculated and overwritten
> > > > +		(visible via the nodeN interfaces) whenever new bandwidth data
> > > > +		is made available either during boot or hotplug events.
> > > > +
> > > > +		In manual mode, node weights can only be updated by the user.
> > > > +		If a node is hotplugged while the user is in manual mode,
> > > > +		the node will have a default weight of 1.
> > > > +
> > > > +		Modes can be changed by writing either "auto" or "manual" to the
> > > > +		interface. All other strings will be ignored, and -EINVAL will
> > > > +		be returned. If "auto" is written to the interface but the
> > > > +		recalculation / updates fail at any point (-ENOMEM or -ENODEV)
> > > > +		then the mode will remain in manual mode.
> > > > +
> > > > +		Writing a new weight to a node directly via the nodeN interface
> > > > +		will also automatically update the system to manual mode.
> > > IMHO, this interface is somewhat hard to be used.  Users need to
> > > know
> > > which value is legal.  So, this will become something like,
> > > $ cat mode
> > > auto [manual]
> > > $ echo auto > mode
> > > $ cat mode
> > > [auto] manual
> >
> > This is exactly I internally proposed to Hyeonggon, but couldn't share
> > the idea directly here.
> >
> > > Unless it's possible we will add more modes in the future, this is
> > > kind
> > > of overkill for me.  How about something simpler as below?
> > > $ cat auto
> > > true
> > > $ echo 0 > auto
> > > $ cat auto
> > > false
> >
> > That also makes sense, but I feel like somewhat vague what "auto" false
> > means. The "auto" might be better to be "use_hmat" instead and this
> > makes "use_hmat" false more meaningful. "use_hmat_weight" or
> > "use_hmat_info" might be another candidates.
>
> As Gregory pointed out in another email.  hmat isn't good because it's
> platform dependent.  We may use something else to get default weights on
> another platform.

Sorry for the late reply.  I prefered "mode" contains auto/manual and
"hmat" names were my second thought, which may not be proper here as you
mentioned.

> I'm open to other platform independent naming.  For example, use_default.

I'm also fine to your another proposal "auto" with Y/N, which is used in
v4.

> [snip]
>
> ---
> Best Regards,
> Huang, Ying

Thanks,
Honggyu