Messages in this thread | | | Date | Mon, 24 Apr 2006 22:43:14 -0700 | From | Keshavamurthy Anil S <> | Subject | Re: [(take 2)patch 7/7] Notify page fault call chain |
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On Tue, Apr 25, 2006 at 11:10:59AM +1000, Keith Owens wrote: > bibo mao (on Mon, 24 Apr 2006 17:19:01 +0800) wrote: > >I have some questions about page fault call chain. > >1) Can kprobe_exceptions_notify be divided into two sub-functions, one > >is for die call chain, which handles DIE_BREAK/DIE_FAULT trap, the other > >is specially for DIE_PAGE_FAULT trap. > > I asked the same question, Anil said that would/could be done in a > later set of patches, but did not want to change too much code in one > go.
I don't think it is necessary to split kprobe_exception_notify(). All it is having is a simple switch case and based on the swich case it takes appropriate actions.
> > >2) page_fault_notifier is conditionally registered/unregistered in this > >patch, notify_page_fault(DIE_PAGE_FAULT...) is unconditionally called in > > ia64_do_page_fault() function. I do not know whether it is possible to > >unconditionally register page_fault_notifier() call chain, but > >conditionally call notify_page_fault(DIE_PAGE_FAULT...) function. > > Only by putting extra code at the site of notify_page_fault(). That > would introduce a race against kprobes unregistering a user space > probe. The race is probably safe, but why risk it?
Their is no race while we call unregister_page_fault_notifier(), as we unregister only after the last probe is removed and after synchronized_sched() is done which guarantees that all the probes have completly finished executing. > > >3) I do know whether there are other conditions like kdb/kgdb which need > >call page fault call chain when page fault happens. If only kprobe need > >handle page fault, then I think kprobe_exceptions_notify can be called > >directly in ia64_do_page_fault() function. Of course, the call chain > >method is more convenient and easy to extend for other fault causes(like > >kdb/kgdb). > > Only kprobes needs the page fault handler. > > Calling kprobe_exceptions_notify() directly would work but again it > introduces races. The register and unregister are atomic, and remember
Calling kprobe_exception_notify() directly can be made to work with out any races if needed. Not sure if calling directly will have any significant performance improvement over current non-overloaded call chain notifications.
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