On 6/8/22 4:21 AM, Tim Chen wrote:
On Fri, 2022-06-03 at 19:12 +0530, Aneesh Kumar K.V wrote:+int next_demotion_node(int node) +{ + struct demotion_nodes *nd; + int target, nnodes, i; + + if (!node_demotion) + return NUMA_NO_NODE; + + nd = &node_demotion[node]; + + /* + * node_demotion[] is updated without excluding this + * function from running. + * + * Make sure to use RCU over entire code blocks if + * node_demotion[] reads need to be consistent. + */ + rcu_read_lock(); + + nnodes = nodes_weight(nd->preferred); + if (!nnodes) + return NUMA_NO_NODE; + + /* + * If there are multiple target nodes, just select one + * target node randomly. + * + * In addition, we can also use round-robin to select + * target node, but we should introduce another variable + * for node_demotion[] to record last selected target node, + * that may cause cache ping-pong due to the changing of + * last target node. Or introducing per-cpu data to avoid + * caching issue, which seems more complicated. So selecting + * target node randomly seems better until now. + */ + nnodes = get_random_int() % nnodes; + target = first_node(nd->preferred); + for (i = 0; i < nnodes; i++) + target = next_node(target, nd->preferred);We can simplify the above 4 lines. target = node_random(nd->preferred); There's still a loop overhead though :(
Will fix in next update.
+ + rcu_read_unlock(); + + return target; +} +
-aneesh
