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Re: [Xen-devel] Re: [PATCH] Two patches fixing regression introduced by

To: "H. Peter Anvin" <hpa@xxxxxxxxx>
Subject: Re: [Xen-devel] Re: [PATCH] Two patches fixing regression introduced by 'x86-64, mm: Put early page table high'
From: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Date: Mon, 2 May 2011 14:08:02 -0400
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, yinghai@xxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, stefano.stabellini@xxxxxxxxxxxxx
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On Mon, May 02, 2011 at 10:31:21AM -0700, H. Peter Anvin wrote:
> On 05/02/2011 10:22 AM, Konrad Rzeszutek Wilk wrote:
> > 
> > But we haven't come up with an acceptable general solution yet, so this
> > patchset provides a workaround for the problem. Peter, Yinghai - what would 
> > be
> > the best forum/email/conference to hammer out a general solution for this?
> > 
> > Currently, there are couple of ways of fixing this:
> >  - use pvops hooks: 
> > http://marc.info/?i=1302607192-21355-2-git-send-email-stefano.stabellini@xxxxxxxxxxxxx
> >  - have a workaround in Xen MMU's early bootup code (which is what these
> >    two patches to this email have).
> >  - or remove the patch introducing the regression altogether.
> > 
> > Foremost important is to fix the regression, and attached patches 
> > achieve that. I want to remove this workaround patch when we
> > hammer out more appropriate semantics for the page table creation - but
> > that will take some time and the runway to do that in 2.6.39 is gone.
> > 
> My inclination would be to apply your workaround -- are there any
> adverse effects to doing that?

There is a bootup slowdown (not noticeable). That is because we call the
'memblock_find_range' function on every PTE table creation (only during
bootup of course). 

Testing wise, on the machines on which the regression occurred, with these two
patches the regression disappears - so that is a good sign. I am testing
it on some more today to assure myself I am not missing anything.

>       -hpa
> [Sorry if I have missed any emails recently... apparently my email was
> significantly on the fritz over the last few days.]

Yikes - I hate when that happens. I was wondering why you went so silent
on some of the emails.

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