Re: [PATCH v5 1/9] mm/demotion: Add support for explicit memory tiers

[Ying Huang]

On Thu, 2022-06-16 at 10:17 +0530, Aneesh Kumar K V wrote:
> On 6/16/22 9:15 AM, Wei Xu wrote:
> > On Wed, Jun 15, 2022 at 6:11 PM Ying Huang <ying.huang@xxxxxxxxx> wrote:
> > > 
> > > On Tue, 2022-06-14 at 14:56 -0400, Johannes Weiner wrote:
> > > > On Tue, Jun 14, 2022 at 01:31:37PM +0530, Aneesh Kumar K V wrote:
> 
> ....
> 
> > > As Jonathan Cameron pointed, we may need the memory tier ID to be
> > > stable if possible.  I know this isn't a easy task.  At least we can
> > > make the default memory tier (CPU local DRAM) ID stable (for example
> > > make it always 128)?  That provides an anchor for users to understand.
> > 
> > One of the motivations of introducing "rank" is to allow memory tier
> > ID to be stable, at least for the well-defined tiers such as the
> > default memory tier.  The default memory tier can be moved around in
> > the tier hierarchy by adjusting its rank position relative to other
> > tiers, but its device ID can remain the same, e.g. always 1.
> > 
> 
> With /sys/devices/system/memtier/default_tier userspace will be able query
> the default tier details.
> 

Yes.  This is a way to address the memory tier ID stability issue too. 
Anther choice is to make default_tier a symbolic link.


Best Regards,
Huang, Ying