* Mathieu Desnoyers <[email protected]> wrote:
> > > Then you lose the ability to trace in-kernel minor page faults.
> >
> > that's wrong, minor pagefaults go through __handle_mm_fault() just as
> > much.
> >
>
> Hi Ingo,
>
> On a 2.6.17 kernel tree :
> It seems like a shortcut path that will never call __handle_mm_fault.
> This path is precisely used to handle vmalloc faults.
yes, but you said "minor fault", not "vmalloc fault".
minor faults are the things that happen when a task does read-after-COW
or read-mmap-ed-pagecache-page, and they very much go through
__handle_mm_fault().
vmalloc faults are extremely rare, x86-specific and they are a pure
kernel-internal matter. (I'd never want to trace them, especially if it
pushes tracepoints into every architecture's page fault handler. I
implemented the initial version of them IIRC, but my memory fails
precisely why. I think it was 4:4 related, but i'm unsure.)
(i now realize that above you said "in-kernel minor faults" - under that
you meant vmalloc faults?)
Ingo
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