Re: [PATCH v5 2/9] mm/demotion: Expose per node memory tier to sysfs

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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.


+		if (node_isset(node, memtier->nodelist))
+			return memtier;
+	}
+	return NULL;
+}
+


Tim


-aneesh





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