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From: David Rientjes on 8 Mar 2010 16:30
On Mon, 8 Mar 2010, Miao Xie wrote:

> Changes from V1 to V2:
> - cleanup two unnecessary smp_wmb() at cpuset_migrate_mm()
>

This patch is already in -mm without this update, so it's probably better
to make this an incremental series basedo n mmotm-2010-03-04-18-05 or
later.

> @@ -2090,15 +2086,19 @@ static int cpuset_track_online_cpus(struct notifier_block *unused_nb,
> static int cpuset_track_online_nodes(struct notifier_block *self,
> unsigned long action, void *arg)
> {
> + nodemask_t oldmems;
> +
> cgroup_lock();
> switch (action) {
> case MEM_ONLINE:
> - case MEM_OFFLINE:
> + oldmems = top_cpuset.mems_allowed;
> mutex_lock(&callback_mutex);
> top_cpuset.mems_allowed = node_states[N_HIGH_MEMORY];
> mutex_unlock(&callback_mutex);
> - if (action == MEM_OFFLINE)
> - scan_for_empty_cpusets(&top_cpuset);
> + update_tasks_nodemask(&top_cpuset, &oldmems, NULL);
> + break;
> + case MEM_OFFLINE:
> + scan_for_empty_cpusets(&top_cpuset);
> break;
> default:
> break;

This looks wrong, why isn't top_cpuset.mems_allowed updated for
MEM_OFFLINE? If you're going to update it when a new node comes online
for (struct memory_notify *)arg->status_change_nid is >= 0, then it should
be removed from the nodemask when offlined as well. You'd be calling
scan_for_empty_cpusets() needlessly in this code since it'll never change
under your hotplug code.
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From: Miao Xie on 8 Mar 2010 20:30
on 2010-3-9 5:22, David Rientjes wrote:
> On Mon, 8 Mar 2010, Miao Xie wrote:
>
>> Changes from V1 to V2:
>> - cleanup two unnecessary smp_wmb() at cpuset_migrate_mm()
>>
>
> This patch is already in -mm without this update, so it's probably better
> to make this an incremental series basedo n mmotm-2010-03-04-18-05 or
> later.

ok, I'll do it.

>
>> @@ -2090,15 +2086,19 @@ static int cpuset_track_online_cpus(struct notifier_block *unused_nb,
>> static int cpuset_track_online_nodes(struct notifier_block *self,
>> unsigned long action, void *arg)
>> {
>> + nodemask_t oldmems;
>> +
>> cgroup_lock();
>> switch (action) {
>> case MEM_ONLINE:
>> - case MEM_OFFLINE:
>> + oldmems = top_cpuset.mems_allowed;
>> mutex_lock(&callback_mutex);
>> top_cpuset.mems_allowed = node_states[N_HIGH_MEMORY];
>> mutex_unlock(&callback_mutex);
>> - if (action == MEM_OFFLINE)
>> - scan_for_empty_cpusets(&top_cpuset);
>> + update_tasks_nodemask(&top_cpuset, &oldmems, NULL);
>> + break;
>> + case MEM_OFFLINE:
>> + scan_for_empty_cpusets(&top_cpuset);
>> break;
>> default:
>> break;
>
> This looks wrong, why isn't top_cpuset.mems_allowed updated for
> MEM_OFFLINE? If you're going to update it when a new node comes online
> for (struct memory_notify *)arg->status_change_nid is >= 0, then it should
> be removed from the nodemask when offlined as well. You'd be calling
> scan_for_empty_cpusets() needlessly in this code since it'll never change
> under your hotplug code.

scan_for_empty_cpusets() will update top_cpuset.mems_allowed when doing MEM_OFFLINE.

The comment of this source is necessary. I'll add it.

Thanks!
Miao

>
>


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