Re: [PATCH 1/5] cpuset memory spread basic implementation

[Ingo Molnar <mingo@elte.hu>]

* Paul Jackson <pj@sgi.com> wrote:

> Ingo asked:
> > so in practice, the memory spreading is in fact a global setting, used
> > by all cpusets that matter? 
> 
> I don't know if that is true or not.
> 
> I'll have to ask my field engineers, who actually have experience
> with a variety of customer workloads.
> 
> ... well, I do have partial knowledge of this.
> 
> When I was coding this, I suggested that instead of picking some of the
> slab caches to memory spread, we pick them all, as that would be easier
> to code.
> 
> That suggestion was shot down by others more experienced within SGI, 
> as some slab caches hold what is essentially per-thread data, that is 
> fairly hot in the thread context that allocated it.  Spreading that 
> data would quite predictably increase cross-node bus traffic, which is 
> bad.

yes, but still that is a global attribute: we know that those slabs are 
fundamentally per-thread. They wont ever be non-per-thread. So the 
decision could be made via a per-slab attribute, that is picked by 
kernel developers (initially you). The pagecache would be spread-out if
this .config option is specified. This makes it a much cleaner static
'kernel fairness policy' thing, instead of a fuzzier userspace thing. 

	Ingo