Re: [RFC][PATCH 00/26] sched/numa

Peter Zijlstra
2012-03-19T13:27:13Z

On Mon, 2012-03-19 at 14:04 +0100, Andrea Arcangeli wrote:

> About the cost of the actual pagetable scanner, you're not being
> rational about it. You should measure it for once, take khugepaged
> make it scan 1G of memory per millisecond and measure the cost.

Death by a thousand cuts..

> You keep complaining about the unaccountability of the pagetable
> scanners in terms of process load, and that's a red herring as far as
> I can tell. The irqs and ksoftirqd load in a busy server, is likely
> much higher than whatever happens at the pagetable scanner level (sure
> thing for khugepaged and by an huge order of magnitude so).

Who says I agree with ksoftirqd? I would love to get rid of all things
softirq. And I also think workqueues are over-/ab-used.

> I don't
> think this is a relevant concern anyway because the pagetable scanners
> go over all memory in a equal amount so the cost would be evenly
> distributed for all processes over time (the same cannot be said about
> the irqs and ksoftrqid that will benefit only a few processes doing
> I/O).

So what about the case where all I do is compile kernels and we already
have near perfect locality because everything is short running? You're
still scanning that memory, and I get no benefit.