Re: [PATCH v5 2/9] mm/demotion: Expose per node memory tier to sysfs
From: Aneesh Kumar K V
Date: Wed Jun 08 2022 - 12:16:13 EST
On 6/8/22 9:36 PM, Tim Chen wrote:
On Wed, 2022-06-08 at 10:25 +0530, Aneesh Kumar K V wrote:
On 6/8/22 1:45 AM, Tim Chen wrote:
On Fri, 2022-06-03 at 19:12 +0530, Aneesh Kumar K.V wrote:
+static struct memory_tier *__node_get_memory_tier(int node)
+{
+ struct memory_tier *memtier;
+
+ list_for_each_entry(memtier, &memory_tiers, list) {
We could need to map node to mem_tier quite often, if we need
to account memory usage at tier level. It will be more efficient
to have a pointer from node (pgdat) to memtier rather
than doing a search through the list.
That is something I was actively trying to avoid. Currently all struct
memory_tier references are with memory_tier_lock mutex held. That
simplify the locking and reference counting.
As of now we are able to implement all the required interfaces without
pgdat having pointers to struct memory_tier. We can update pgdat with
memtier details when we are implementing changes requiring those. We
could keep additional memtier->dev reference to make sure memory tiers
are not destroyed while other part of the kernel is referencing the
same. But IMHO such changes should wait till we have users for the same.
I think we should have an efficient mapping from node to memtier from
the get go. There are many easily envisioned scenarios where
we need to map from node to memtier, which Ying pointed out.
I did an initial implementation here. We need to make sure we can access
NODE_DATA()->memtier lockless. Can you review the changes here
https://lore.kernel.org/linux-mm/87sfoffcfz.fsf@xxxxxxxxxxxxx
-aneesh