Re: Replacement for page fault notifiers?

Matt Mackall
2008-01-10T02:03:49Z

On Wed, 2008-01-09 at 16:42 -0800, Arjan van de Ven wrote:
> On Wed, 9 Jan 2008 20:22:54 +0000
> Christoph Hellwig <hch@infradead.org> wrote:
>
> > On Thu, Jan 10, 2008 at 06:58:23AM +1100, Benjamin Herrenschmidt
> > wrote:
> > > It's a sane thing to do, Christoph, I don't think it's a
> > > unreasonable request to put the hooks back in.
> >
> > As said a few times before there's simply no way we're going to put
> > exactly that crap back. For one the patch removed a whole lot of
> > crud from the kprobes code that simply isn't going to come back just
> > because there are some pagefault notifiers. Second the page fault
> > notifiers were horribly implemented and quite inefficient. And third
> > we're not going to put something in just for out of tree code.
> >
>
> I'm btw all in favor of making mmio tracing full fledged kernel infrastructure.
> This doesn't mean "notifier" imo; this means a real flag in the struct page,
> and then the page fault code can do
>
> if (page->flags & FLAG_MMIO_TRACED)
> mmio_trace(page, regs, whatever..);

That makes it way too easy for drivers of questionable legality to just
clear that bit. Also, we've got a shortage of page bits, etc.

--
Mathematics is the supreme nostalgia of our time.