Re: cpusets vs. mempolicy and how to get interleaving

[David Rientjes <rientjes@google.com>]

On Mon, 20 Aug 2007, Ethan Solomita wrote:

> > Like I've already said, there is absolutely no reason to add a new MPOL
> > variant for this case.  As Christoph already mentioned, PF_SPREAD_PAGE gets
> > similar results.  So just modify mpol_rebind_policy() so that if
> > /dev/cpuset/<cpuset>/memory_spread_page is true, you rebind the interleaved
> > nodemask to all nodes in the new nodemask.  That's the well-defined cpuset
> > interface for getting an interleaved behavior already.
> 
> 	memory_spread_page is only for file-backed pages, not anon pages.

Please read what I said above, all you have to do is modify 
mpol_rebind_policy() so that if /dev/cpuset/<cpuset>/memory_spread_page is 
true, you rebind the interleaved nodemask to all nodes in the new 
nodemask.

This only happens for the MPOL_INTERLEAVE case because the application has 
made it quite clear through set_mempolicy(MPOL_INTERLEAVE, ...) that it 
wants this behavior.

	int cpuset_is_spread_page(struct task_struct *task)
	{
		int ret;
		task_lock(task);
		ret = is_spread_page(task->cpuset);
		task_unlock(task);
		return ret;
	}

	void mpol_rebind_policy(struct mempolicy *pol, const nodemask_t *newmask)
	{
		...
		case MPOL_INTERLEAVE:
			if (cpuset_is_spread_page(current))
				pol->v.nodes = *newmask;
			else {
				nodes_remap(tmp, pol->v.nodes, *mpolmask, *newmask);
				pol->v.nodes = tmp;
			}
			...
		...
	}

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