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SubjectRe: [patch -mm] cpusets: add memory_slab_hardwall flag
On Mon, 9 Mar 2009, KOSAKI Motohiro wrote:

> Hmmm,
> this description only explay how to implement this.
> but no explain why this patch is useful.
>
> Could you please who and why need it?
>

The change to Documentation/cgroups/cpusets.txt should have explained it.

This is for two cases: true memory isolation (now including slab
allocations at the object level) and NUMA optimizations.

Prior to this change, it was possible for slabs to be allocated in a
cpuset while its objects were largely consumed by disjoint cpusets. We
can fix that by only allocating objects from slabs that are found on
current->mems_allowed. While this incurs a performance penalty, some
users may find that true isolation outweighs the cache optimizations.

It is also helpful for long-lived objects that require NUMA affinity to a
certain cpu or group of cpus. That is, after all, the reasoning behind
cpusets in the first place. If slab objects were all allocated from a
node with remote affinity to the cpus that will be addressing it, it
negates a significant advantage that cpusets provides to the user.


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