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SubjectRe: [PATCH 32/52] sched: Track groups of shared tasks
On 12/02/2012 01:43 PM, Ingo Molnar wrote:

> This is not entirely correct as this task might have scheduled or
> migrate ther - but statistically there will be correlation to the
^^^^ there?

> tasks that we share memory with, and correlation is all we need.
>
> We map out the relation itself by filtering out the highest address
> ask that is below our own task address, per working set scan
^^^ task?
> iteration.

> @@ -906,23 +945,122 @@ out_backoff:
> }
>
> /*
> + * Track our "memory buddies" the tasks we actively share memory with.
> + *
> + * Firstly we establish the identity of some other task that we are
> + * sharing memory with by looking at rq[page::last_cpu].curr - i.e.
> + * we check the task that is running on that CPU right now.
> + *
> + * This is not entirely correct as this task might have scheduled or
> + * migrate ther - but statistically there will be correlation to the
^^^^ there

> + * tasks that we share memory with, and correlation is all we need.
> + *
> + * We map out the relation itself by filtering out the highest address
> + * ask that is below our own task address, per working set scan
^^^ task?

If that word is "task", the comment makes sense. If it is
something else, I'm back to square one on what the code does :)


> void task_numa_fault(int node, int last_cpu, int pages)
> {
> struct task_struct *p = current;
> int priv = (task_cpu(p) == last_cpu);
> + int idx = 2*node + priv;
>
> if (unlikely(!p->numa_faults)) {
> - int size = sizeof(*p->numa_faults) * 2 * nr_node_ids;
> + int entries = 2*nr_node_ids;
> + int size = sizeof(*p->numa_faults) * entries;
>
> - p->numa_faults = kzalloc(size, GFP_KERNEL);
> + p->numa_faults = kzalloc(2*size, GFP_KERNEL);

So we multiply nr_node_ids by 2. Twice.

That kind of magic deserves a comment explaining how
and why. How about:

/*
* We track two arrays with private and shared faults
* for each NUMA node. The p->numa_faults_curr array
* is allocated at the same time as the p->numa_faults
* array.
*/
int size = sizeof(*p->numa_faults) * 4 * nr_node_ids;

> if (!p->numa_faults)
> return;
> + /*
> + * For efficiency reasons we allocate ->numa_faults[]
> + * and ->numa_faults_curr[] at once and split the
> + * buffer we get. They are separate otherwise.
> + */
> + p->numa_faults_curr = p->numa_faults + entries;
> }




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