linux-kernel - Re: [RFC] page fault retry with NOPAGE

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Message-Id: <1158880165.26347.132.camel@localhost.localdomain>
Date:	Fri, 22 Sep 2006 09:09:25 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Andrew Morton <akpm@...l.org>
Cc:	Mike Waychison <mikew@...gle.com>, linux-mm@...ck.org,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...l.org>
Subject: Re: [RFC] page fault retry with NOPAGE_RETRY

On Thu, 2006-09-21 at 15:41 -0700, Andrew Morton wrote:
> On Fri, 22 Sep 2006 08:05:04 +1000
> Benjamin Herrenschmidt <benh@...nel.crashing.org> wrote:
> 
> > > So I think there's a nasty DoS here if we permit infinite retries.  But
> > > it's not just that - there might be other situations under really heavy
> > > memory pressure where livelocks like this can occur.  It's just a general
> > > robustness-of-implementation issue.
> > 
> > Got it. Now, changing args to no_page() will be a pretty big task....
> > 
> 
> Not as big as removing the pt_regs arg from every interrupt handler ;)

Which is a change I'm not 100% convinced about btw ... I remember
actually using that in a few occasions... mostly for debugging though.
Bah, anyway, I suppose we can always have a per-cpu global with the last
irq pt_regs pointer if really needed for debug.
 
> But pretty mechanical.  Problem is, I don't think we have our mechanic.

Yup, we would need to decide what to put in there....

Ben.


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