Alistair Popple <apopple@xxxxxxxxxx> writes:
....
> + */
>> +static void establish_migration_targets(void)
>> +{
>> + struct memory_tier *memtier;
>> + struct demotion_nodes *nd;
>> + int target = NUMA_NO_NODE, node;
>> + int distance, best_distance;
>> + nodemask_t used;
>> +
>> + if (!node_demotion || !IS_ENABLED(CONFIG_MIGRATION))
>
> Does it make sense to include the memory tiering/demotion code if
> CONFIG_MIGRATION isn't enabled? From what I can tell none of the
> information established here is used if CONFIG_MIGRATION isn't enabled,
> so it would be better to remove the IS_ENABLED checks and not include
> the code at all.
We use the same function/codepath for updating top_tier details. We
would want to get node_is_toptier() to work even with CONFIG_MIGRATION
disabled?
>
>> + return;
>> +
>> + disable_all_migrate_targets();
>> +
>> + for_each_node_state(node, N_MEMORY) {
>> + best_distance = -1;
>> + nd = &node_demotion[node];
>> +
>> + memtier = __node_get_memory_tier(node);
>> + if (!memtier || list_is_last(&memtier->list, &memory_tiers))
>> + continue;
>> + /*
>> + * Get the next memtier to find the demotion node list.
>> + */
>> + memtier = list_next_entry(memtier, list);
>> +
>> + /*
>> + * find_next_best_node, use 'used' nodemask as a skip list.
>> + * Add all memory nodes except the selected memory tier
>> + * nodelist to skip list so that we find the best node from the
>> + * memtier nodelist.
>> + */
>> + nodes_andnot(used, node_states[N_MEMORY], memtier->nodelist);
>> +
>> + /*
>> + * Find all the nodes in the memory tier node list of same best distance.
>> + * add them to the preferred mask. We randomly select between nodes
>> + * in the preferred mask when allocating pages during demotion.
>> + */
>> + do {
>> + target = find_next_best_node(node, &used);
>> + if (target == NUMA_NO_NODE)
>> + break;
>> +
>> + distance = node_distance(node, target);
>> + if (distance == best_distance || best_distance == -1) {
>> + best_distance = distance;
>> + node_set(target, nd->preferred);
>> + } else {
>> + break;
>> + }
>> + } while (1);
>> + }
>> +}
>> +
.....
-aneesh
