From: Wei Yang <richardw.yang@xxxxxxxxxxxxxxx> Subject: mm/vmscan.c: remove cpu online notification for now kswapd kernel thread starts either with a CPU affinity set to the full cpu mask of its target node or without any affinity at all if the node is CPUless. There is a cpu hotplug callback (kswapd_cpu_online) that implements an elaborate way to update this mask when a cpu is onlined. It is not really clear whether there is any actual benefit from this scheme. Completely CPU-less NUMA nodes rarely gain a new CPU during runtime. Drop the code for that reason. If there is a real usecase then we can resurrect and simplify the code. [mhocko@xxxxxxxx rewrite changelog] Link: http://lkml.kernel.org/r/20200218224422.3407-1-richardw.yang@xxxxxxxxxxxxxxx Suggested-by: Michal Hocko <mhocko@xxxxxxxx> Signed-off-by: Wei Yang <richardw.yang@xxxxxxxxxxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> Cc: David Rientjes <rientjes@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/vmscan.c | 27 +-------------------------- 1 file changed, 1 insertion(+), 26 deletions(-) --- a/mm/vmscan.c~mm-vmscanc-remove-cpu-online-notification-for-now +++ a/mm/vmscan.c @@ -4030,27 +4030,6 @@ unsigned long shrink_all_memory(unsigned } #endif /* CONFIG_HIBERNATION */ -/* It's optimal to keep kswapds on the same CPUs as their memory, but - not required for correctness. So if the last cpu in a node goes - away, we get changed to run anywhere: as the first one comes back, - restore their cpu bindings. */ -static int kswapd_cpu_online(unsigned int cpu) -{ - int nid; - - for_each_node_state(nid, N_MEMORY) { - pg_data_t *pgdat = NODE_DATA(nid); - const struct cpumask *mask; - - mask = cpumask_of_node(pgdat->node_id); - - if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids) - /* One of our CPUs online: restore mask */ - set_cpus_allowed_ptr(pgdat->kswapd, mask); - } - return 0; -} - /* * This kswapd start function will be called by init and node-hot-add. * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added. @@ -4090,15 +4069,11 @@ void kswapd_stop(int nid) static int __init kswapd_init(void) { - int nid, ret; + int nid; swap_setup(); for_each_node_state(nid, N_MEMORY) kswapd_run(nid); - ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, - "mm/vmscan:online", kswapd_cpu_online, - NULL); - WARN_ON(ret < 0); return 0; } _
