Re: [EXT] Re: [RFC PATCH 0/2] Node migration between memory tiers

[Srinivasulu Thanneeru <sthanneeru.opensrc@micron.com>]

On 12/5/2023 2:05 PM, Michal Hocko wrote:
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> 
> On Tue 05-12-23 01:26:07, Srinivasulu Thanneeru wrote:
>>
>>
>> On 12/4/2023 9:13 PM, Michal Hocko wrote:
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>>> On Fri 01-12-23 03:34:20, sthanneeru.opensrc@micron.com wrote:
>>>> From: Srinivasulu Thanneeru <sthanneeru.opensrc@micron.com>
>>>>
>>>> The memory tiers feature allows nodes with similar memory types
>>>> or performance characteristics to be grouped together in a
>>>> memory tier. However, there is currently no provision for
>>>> moving a node from one tier to another on demand.
>>>
>>> Could you expand on why this is really needed/necessary? What is the
>>> actual usecase?
>>
>> Hi Michal Hock,
>>
>> Following two use-cases we have observed.
>> 1. It is not accurate to group similar memory types in the same tier,
>>     because even similar memory types may have different speed grades.
> 
> Presumably they are grouped based on a HW configuration. Does that mean
> that the configuration is wrong? Are you trying to workaround that by
> this interface?
> 
>> 2. Some systems boots up with CXL devices and DRAM on the same memory-tier,
>> we need a way to move the CXL nodes to the correct tier from the user space.
> 
> Again, could you expand a bit more and explain why this cannot be
> configured automatically?

Yes, in both cases above, if hardware not automatically populated 
properly, in that case this interface would help to correct it from user 
space.

We had observed case-2 in our setups.

> --
> Michal Hocko
> SUSE Labs