Re: [tip:sched/numa] sched/numa: Introduce sys_numa_{t,m}bind()

[Peter Zijlstra]

On Fri, 2012-05-18 at 11:00 -0500, Christoph Lameter wrote:

> Having the page local is a win if there are a sufficient number of
> accesses to amortize the effort to move the page. Given the expensive
> nature of page migration there would need to be a large number of accesses
> to a page to justify the effort.

Right, but this is true of any migration scheme and not specific to MoF.

> > How does it matter how you migrate?
> 
> Migrate on fault incurs two types of costs:
> 
> 1. Unmapping. This results in additional faults to reestablish the ptes.
> 
> 2. Actual lazy migrate. More faults. Now the page needs to be copied to
>    the new node and the actual migration work is done. 

Nah, only the 1 fault is extra. Regular migration already needs to unmap
and copy and reinstate, so the only extra work is the fault to trigger
it.




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