Messages in this thread | | | Subject | Re: [tip:perfcounters/core] x86: Add NMI types for kmap_atomic | From | Peter Zijlstra <> | Date | Mon, 15 Jun 2009 21:00:33 +0200 |
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On Mon, 2009-06-15 at 20:52 +0200, Ingo Molnar wrote: > * Peter Zijlstra <peterz@infradead.org> wrote: > > > 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? > > if (++depth == MAX_DEPTH) { > print_all_entries_and_nasty_warning(); > /* hope we'll live long enough for the syslog to touch disk */ > depth = 0; > }
That will only trigger if we hit it, which will be _very_ rare.
> unbalanced kmap is a bad bug - the easier we make it to catch, the > better. The system wouldnt survive anyway.
My proposed patch validates strict balance of types. But I can easily add the above as well.
By removing the types it becomes very difficult to verify the max depth. I really don't like removing them.
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