On Mon, 2009-06-15 at 20:52 +0200, Ingo Molnar wrote:
> * Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> > On Mon, 2009-06-15 at 20:42 +0200, Ingo Molnar wrote:
> > > * Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> > >
> > > > On Mon, 2009-06-15 at 20:25 +0200, Ingo Molnar wrote:
> > > > > * Peter Zijlstra <peterz@xxxxxxxxxxxxx> 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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