Messages in this thread | | | Date | Mon, 15 Jun 2009 20:42:17 +0200 | From | Ingo Molnar <> | Subject | Re: [tip:perfcounters/core] x86: Add NMI types for kmap_atomic |
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* 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 ...
Unbalanced unmaps will be detected under CONFIG_DEBUG_VM: kunmap uses 'page' as a parameter which is checked against the pte entry - they must match.
I.e. it becomes a symmetric and expressive API:
kaddr = kmap_atomic(page); ... kunmap_atomic(page);
Hm?
Ingo
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