Re: [PATCHv2 2/2] tracing,mm - add kernel pagefault tracepoint for x86 & x86_64

Jiri Olsa
2010-11-16T09:23:41Z

On Mon, Nov 15, 2010 at 09:19:20AM -0500, Steven Rostedt wrote:
> On Mon, 2010-11-15 at 14:43 +0100, Frederic Weisbecker wrote:
>
>
> > dotraplinkage void __kprobes
> > do_page_fault(struct pt_regs *regs, unsigned long error_code)
> > {
> > unsigned long address;
> >
> > /* Get the faulting address: */
> > address = read_cr2();
> >
> > trace_mm_pagefault_start(address, error_code);
> > __do_page_fault(regs, address, error_code);
> > trace_mm_pagefault_end(address);
> > }
> >
> >
> > Would you be ok with that?
> >
> > Last thing I worry about is that error_code that is very arch dependent.
> > If someone writes a script that depends on the x86 code, it won't work
> > elsewhere while it's fairly possible to have a generic tracepoint there.
> >
> > So perhaps we rather need a generic enum field instead of the error_code,
> > to express the most interesting specific fault attributes. Than can
> > probably be added later though, once someone really needs it.
> >
> > Hm?
>
> Perhaps we should have:
>
> trace_arch_mm_pagefault_start(address, error_code);
> __do_page_fault(regs, address, error_code);
> trace_mm_pagefault_end(address);
>
>
> Then we have a arch/x86/kernel/trace.c that can map trace_arch_...
> events to generic events. This file will hold the
> trace_mm_pagefault_start(), which is called by
> trace_arch_mm_pagefault_start(). Have a hook that when the
> trace_mm_pagefault_start() is enabled, we also enable
> trace_arch_mm_pagefault_start() that calls this tracepoint. The
> trace_mm_pagefault_start() will then translate the
> trace_arch_mm_pagfault_start() into the generic trace_mm_pagefault_start
> event with the generic error_code that all archs will use.
>
> Reason being, we don't need to do any extra processing in the fast path
> when tracing is not enabled.
>
> Also, I'm going to start working on the stable ABI today.
do you mean stable api for the hook you described above?
or should I come up with smth..

thanks,
jirka