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SubjectRe: [RFC PATCH v4 2/7] mm/demotion: Expose per node memory tier to sysfs
On 5/27/22 7:45 PM, Jonathan Cameron wrote:
> On Fri, 27 May 2022 17:55:23 +0530
> "Aneesh Kumar K.V" <> wrote:
>> From: Jagdish Gediya <>
>> Add support to read/write the memory tierindex for a NUMA node.
>> /sys/devices/system/node/nodeN/memtier
>> where N = node id
>> When read, It list the memory tier that the node belongs to.
>> When written, the kernel moves the node into the specified
>> memory tier, the tier assignment of all other nodes are not
>> affected.
>> If the memory tier does not exist, writing to the above file
>> create the tier and assign the NUMA node to that tier.
> creates
> There was some discussion in v2 of Wei Xu's RFC that what matter
> for creation is the rank, not the tier number.
> My suggestion is move to an explicit creation file such as
> memtier/create_tier_from_rank
> to which writing the rank gives results in a new tier
> with the next device ID and requested rank.

I think the below workflow is much simpler.

:/sys/devices/system# cat memtier/memtier1/nodelist
:/sys/devices/system# cat node/node1/memtier
:/sys/devices/system# ls memtier/memtier*
nodelist power rank subsystem uevent
/sys/devices/system# ls memtier/
default_rank max_tier memtier1 power uevent
:/sys/devices/system# echo 2 > node/node1/memtier

:/sys/devices/system# ls memtier/
default_rank max_tier memtier1 memtier2 power uevent
:/sys/devices/system# cat memtier/memtier1/nodelist
:/sys/devices/system# cat memtier/memtier2/nodelist

ie, to create a tier we just write the tier id/tier index to
node/nodeN/memtier file. That will create a new memory tier if needed
and add the node to that specific memory tier. Since for now we are
having 1:1 mapping between tier index to rank value, we can derive the
rank value from the memory tier index.

For dynamic memory tier support, we can assign a rank value such that
new memory tiers are always created such that it comes last in the
demotion order.


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