linux-kernel - Re: Replacement for page fault notifiers?

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Message-ID: <20080109164241.7daa5770@laptopd505.fenrus.org>
Date:	Wed, 9 Jan 2008 16:42:41 -0800
From:	Arjan van de Ven <arjan@...radead.org>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Christoph Hellwig <hch@...radead.org>,
	Pavel Roskin <proski@....org>, Dave Airlie <airlied@...il.com>,
	Pekka Paalanen <pq@....fi>, linux-kernel@...r.kernel.org,
	jbeulich@...ell.com
Subject: Re: Replacement for page fault notifiers?

On Wed, 9 Jan 2008 20:22:54 +0000
Christoph Hellwig <hch@...radead.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..);

(probably surrounded by a CONFIG_ ifdef)
THis is a TON lighter than a notifier chain, and actually what you want,
you don't really want a notifier, you want a call back when a special kind of
page is touched.


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