Re: [tip:perfcounters/core] x86: Add NMI types for kmap_atomic

[Peter Zijlstra <peterz@infradead.org>]

On Mon, 2009-06-15 at 20:42 +0200, Ingo Molnar wrote:
> * Peter Zijlstra <peterz@infradead.org> wrote:
> 
> > On Mon, 2009-06-15 at 20:25 +0200, Ingo Molnar wrote:
> > > * Peter Zijlstra <peterz@infradead.org> wrote:
> > 
> > > but ... look at the APIs i propose above. We dont need _any_ 
> > > 'types'.
> > > 
> > > That type enumeration is basically an open-coded allocator. If we do 
> > > a _real_ allocator (a balanced stack of atomic kmaps) we dont need 
> > > any of those indices, and all the potential for mismatch goes away 
> > > as well - a stack nests trivially with IRQ and NMI and arbitrary 
> > > other contexts.
> > 
> > You want types because:
> >  - they encode the intent, and can be verified
> >  - they help keep track of the max nesting depth
> > 
> > In the proposed implementation all type code basically falls away 
> > no ! CONFIG_DEBUG_VM, but is kept around for robustness.
> 
> But much of the fragility of the types (and their clumsiness - for 
> example in highpte ops we have to know at which level of the 
> pagetables we are, and use the right kind of index) is _precisely_ 
> because we have the types ...

How will you manage the max depth?