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

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Message-Id: <1199930590.6245.104.camel@cinder.waste.org>
Date:	Wed, 09 Jan 2008 20:03:10 -0600
From:	Matt Mackall <mpm@...enic.com>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.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, 2008-01-09 at 16:42 -0800, Arjan van de Ven wrote:
> 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..);

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.

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