Re: [BUG] set_mempolicy(MPOL_INTERLEAV) cause kernel panic

[KOSAKI Motohiro]

> On Wed, 15 Jul 2009, Lee Schermerhorn wrote:
> 
> > Interestingly, on ia64, the top cpuset mems_allowed gets set to all
> > possible nodes, while on x86_64, it gets set to on-line nodes [or nodes
> > with memory].  Maybe this is a to support hot-plug?
> > 
> 
> numactl --interleave=all simply passes a nodemask with all bits set, so if 
> cpuset_current_mems_allowed includes offline nodes from node_possible_map, 
> then mpol_set_nodemask() doesn't mask them off.
> 
> Seems like we could handle this strictly in mempolicies without worrying 
> about top_cpuset like in the following?

This patch seems band-aid patch. it will change memory-hotplug behavior.
Please imazine following scenario:

1. numactl interleave=all process-A
2. memory hot-add

before 2.6.30:
		-> process-A can use hot-added memory

your proposal patch:
		-> process-A can't use hot-added memory




> ---
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -194,6 +194,7 @@ static int mpol_new_bind(struct mempolicy *pol, const nodemask_t *nodes)
>  static int mpol_set_nodemask(struct mempolicy *pol, const nodemask_t *nodes)
>  {
>  	nodemask_t cpuset_context_nmask;
> +	nodemask_t mems_allowed;
>  	int ret;
>  
>  	/* if mode is MPOL_DEFAULT, pol is NULL. This is right. */
> @@ -201,20 +202,21 @@ static int mpol_set_nodemask(struct mempolicy *pol, const nodemask_t *nodes)
>  		return 0;
>  
>  	VM_BUG_ON(!nodes);
> +	nodes_and(mems_allowed, cpuset_current_mems_allowed,
> +				node_states[N_HIGH_MEMORY]);
>  	if (pol->mode == MPOL_PREFERRED && nodes_empty(*nodes))
>  		nodes = NULL;	/* explicit local allocation */
>  	else {
>  		if (pol->flags & MPOL_F_RELATIVE_NODES)
>  			mpol_relative_nodemask(&cpuset_context_nmask, nodes,
> -					       &cpuset_current_mems_allowed);
> +					       &mems_allowed);
>  		else
>  			nodes_and(cpuset_context_nmask, *nodes,
> -				  cpuset_current_mems_allowed);
> +				  mems_allowed);
>  		if (mpol_store_user_nodemask(pol))
>  			pol->w.user_nodemask = *nodes;
>  		else
> -			pol->w.cpuset_mems_allowed =
> -						cpuset_current_mems_allowed;
> +			pol->w.cpuset_mems_allowed = mems_allowed;
>  	}
>  
>  	ret = mpol_ops[pol->mode].create(pol,



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