Re: [PATCH v6 1/6] mm/mempolicy: Add MPOL_PREFERRED_MANY for multiple preferred nodes

On Thu, Jul 29, 2021 at 06:21:19PM +0200, Michal Hocko wrote:

On Thu 29-07-21 23:12:42, Feng Tang wrote:

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On Thu, Jul 29, 2021 at 03:38:44PM +0200, Michal Hocko wrote:

[...]

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Also the
semantic to give nodes some ordering based on their numbers sounds
rather weird to me.

I agree, and as I admitted in the first reply, this need to be fixed.

OK. I was not really clear that we are on the same page here.

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The semantic I am proposing is to allocate from prefered nodes in
distance order starting from the local node.

So the plan is:
* if the local node is set in 'prefer-many's nodemask, then chose
* otherwise chose the node with the shortest distance to local node
?

Yes and what I am trying to say is that you will achieve that simply by
doing the following in policy_node:
	if (policy->mode == MPOL_PREFERRED_MANY)
		return nd;

One thing is, it's possible that 'nd' is not set in the preferred
nodemask. 

For policy_node(), most of its caller use the local node id as 'nd'
parameter. For HBM and PMEM memory nodes, they are cpuless nodes,
so they will not be a 'local node', but some use cases only prefer
these nodes.

Thanks,
Feng

-- 
Michal Hocko
SUSE Labs