Re: [patch 2/2] slub: enforce cpuset restrictions for cpu slabs

[David Rientjes]

On Tue, 3 Mar 2009, Paul Menage wrote:

> > Unfortunately, we can't add a slab hardwall flag to the cpuset to
> > configure this behavior since that would require locking to dereference
> > in the fastpath.
> >
> 
> I don't think that it would - cgroups and subsystems should be RCU safe.
> 

That would help for cpusets that are looking for NUMA optimizations (i.e. 
probably long-lived objects with local affinity) but would not ensure 
memory isolation from tasks in other exclusive cpusets from allocating on 
my slab.

So to address both NUMA and memory isolation, it seems like we'd need to 
add a `slab_hardwall' flag that would have to be disabled for both cpusets 
(the one hosting the cpu slab and the one allocating an object) to ignore 
the hardwall requirement.

That isn't a very clean solution, but is certainly plausible if 
Christoph's objection is that in the vast majority of multiple cpuset 
systems it is far better to allocate on cpu slabs than for true memory 
isolation or the ability to allocate an object on a specific node (for 
which we currently have no solution) for affinity.
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