linux-kernel - Re: [PATCH] mmu_notifier, kvm: Introduce dirty bit tracking in spte and mmu notifier to help KSM dirty bit tracking

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Message-ID: <BANLkTik2P95vxuUkRi5C+=Xaw7TkE3JR2w@mail.gmail.com>
Date:	Thu, 23 Jun 2011 08:14:28 +0800
From:	Nai Xia <nai.xia@...il.com>
To:	Andrea Arcangeli <aarcange@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Izik Eidus <izik.eidus@...ellosystems.com>,
	Hugh Dickins <hughd@...gle.com>,
	Chris Wright <chrisw@...s-sol.org>,
	Rik van Riel <riel@...hat.com>,
	linux-mm <linux-mm@...ck.org>,
	Johannes Weiner <hannes@...xchg.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	kvm <kvm@...r.kernel.org>
Subject: Re: [PATCH] mmu_notifier, kvm: Introduce dirty bit tracking in spte
 and mmu notifier to help KSM dirty bit tracking

On Thu, Jun 23, 2011 at 7:44 AM, Andrea Arcangeli <aarcange@...hat.com> wrote:
> On Thu, Jun 23, 2011 at 07:19:06AM +0800, Nai Xia wrote:
>> OK, I'll have a try over other workarounds.
>> I am not feeling good about need_pte_unmap myself. :-)
>
> The usual way is to check VM_HUGETLB in the caller and to call another
> function that doesn't kmap. Casting pmd_t to pte_t isn't really nice
> (but hey we're also doing that exceptionally in smaps_pte_range for
> THP, but it safe there because we're casting the value of the pmd, not
> the pointer to the pmd, so the kmap is done by the pte version of the
> caller and not done by the pmd version of the caller).
>
> Is it done for migrate? Surely it's not for swapout ;).

Thanks for the hint. :-)

You know, another thing I am worried about is that I think I
did make page_check_address()  return a pmd version for skipping the
tail subpages ...
I did detecte a schedule in atomic if I kunmap() the returned value. :-(

>
>> Thanks for viewing!
>
> You're welcome!
>
> JFYI I'll be offline on vacation for a week, starting tomorrow, so if
> I don't answer in the next few days that's the reason but I'll follow
> the progress in a week.

Have a nice vacation man! Enjoy the sunlight, we all have enough
of code in rooms. ;-)


Thanks,
Nai

>
> Thanks!
> Andrea
>
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