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SubjectRe: [BUG] set_mempolicy(MPOL_INTERLEAV) cause kernel panic
Date
> 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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