Re: [RFC 4/9] Atomic reclaim: Save irq flags in vmscan.c

Christoph Lameter
2007-08-14T22:42:19Z

On Wed, 15 Aug 2007, Andi Kleen wrote:

> > Ok I have a vague idea on how this could but its likely that the
> > changes make things worse rather than better. Additional reference to a
> > new cacheline (per cpu but still), preempt disable. Lots of code at all
> > call sites. Interrupt enable/disable is quite efficient in recent
> > processors.
>
> The goal of this was not to be faster than interrupt disable,
> but to avoid the interrupt latency impact. This might be a problem
> when spending a lot of time inside the locks.

Both. They need to be fast too and not complicate the kernel too much. I
have not seen a serious holdoff case. The biggest issue is still the
zone->lru lock but interrupts are always disabled for that one already.