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Re: [Xen-devel] Fwd: Re: struct page field arrangement

To: Keir Fraser <keir@xxxxxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxxxx>
Subject: Re: [Xen-devel] Fwd: Re: struct page field arrangement
From: Keir Fraser <keir@xxxxxxxxxxxxx>
Date: Fri, 16 Mar 2007 12:25:25 +0000
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On 16/3/07 12:11, "Keir Fraser" <keir@xxxxxxxxxxxxx> wrote:

>> page_referenced_one() in mm/rmap.c). If this happens when
>> xen_pgd_unpin() has already passed the respective pte page, but
>> mm_walk() hasn't reached the page, yet, the update will fail (if done
>> directly, ptwr will no pick this up, and if done through a hypercall, the
>> call would fail, likely producing a BUG()).
> What kind of stress test did you run? I was expecting that unpin would be
> okay because we only call mm_unpin() from _arch_exit_mmap() if the mm_count
> is 1 (which I believe means the mm is not active in any task).

And actually the pinning happens on activate_mm() in most cases, which I
would expect to be 'early enough' since noone can run on the mm before that?

If you've managed to provoke bugs then that's very interesting (and scary)!

I suppose if I understand the rmap case correctly, we're still susceptible
to the paging kernel thread trying to page things out at any time? Is that
what you think you've been seeing go wrong?

 -- Keir

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