[ltt-dev] [PATCH] Fix dirty page accounting in redirty_page_for_writepage()

[mingo@elte.hu (Ingo Molnar)]

* Christoph Lameter <cl at linux.com> wrote:

> On Thu, 30 Apr 2009, Ingo Molnar wrote:
> 
> > > Yes but sometimes you are already irq safe and such a fallback
> > > would create significant irq/enable/disable stack operations etc
> > > overhead for architectures that are using the fallback.
> >
> > It's a fallback slowpath - non-x86 architectures should still fill
> > in a real implementation of course.
> 
> Arch code cannot provide an effective implementation since they
> always have to assume that interupts need to be disabled if we stay with
> the current implementation.
> 
> > So we first have to see the list of architectures that _cannot_
> > implement an irq-safe op here via a single machine instruction.
> > x86, ia64 and powerpc should be fine.
> 
> Look at Ia64, sparc, s/390, powerpc. They can fall back to atomic 
> ops but those are very ineffective on some of these platforms. 
> Since these are performance critical they will need to be 
> optimized depending on the context of their use in the core.

Could you cite a specific example / situation where you'd use __xxx 
ops?

	Ingo