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SubjectRe: [BUG] set_mempolicy(MPOL_INTERLEAV) cause kernel panic
On Fri, 17 Jul 2009 09:04:46 +0900 (JST)
KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> wrote:

> > 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
>

IMHO, the application itseld should be notifed to change its mempolicy by
hot-plug script on the host. While an application uses interleave, a new node
hot-added is just a noise. I think "How pages are interleaved" should not be
changed implicitly. Then, checking at set_mempolicy() seems sane. If notified,
application can do page migration and rebuild his mapping in ideal way.

BUT I don't linke init->mem_allowed contains N_POSSIBLE...it should be initialized
to N_HIGH_MEMORY, IMHO.

Thanks,
-Kame




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