On Mon, 14 Oct 2013 14:04:56 -0600 Toshi Kani <toshi.kani@xxxxxx> wrote:
> After a system booted, N_CPU is not set to any node as has_cpu
> shows an empty line.
>
> # cat /sys/devices/system/node/has_cpu
> (show-empty-line)
>
> setup_vmstat() registers its CPU notifier callback,
> vmstat_cpuup_callback(), which marks N_CPU to a node when
> a CPU is put into online. However, setup_vmstat() is called
> after all CPUs are launched in the boot sequence.
>
> Change setup_vmstat() to mark N_CPU to the nodes with online
> CPUs at boot.
>
> ...
>
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -1276,8 +1276,10 @@ static int __init setup_vmstat(void)
>
> register_cpu_notifier(&vmstat_notifier);
>
> - for_each_online_cpu(cpu)
> + for_each_online_cpu(cpu) {
> start_cpu_timer(cpu);
> + node_set_state(cpu_to_node(cpu), N_CPU);
> + }
> #endif
> #ifdef CONFIG_PROC_FS
> proc_create("buddyinfo", S_IRUGO, NULL, &fragmentation_file_operations);
This seems a bit hacky. Would it not be better to register
vmstat_notifier() before bringing up CPUs?
And this patch might be racy as well - what happens if a CPU comes up
and goes down again before setup_vmstat() is called?
(Where does N_CPU get cleared? It doesn't, afaict. Should we clear it
if a node's final CPU goes offline?)
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