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: <BANLkTim85ghrK9D4f19Pt5v1+HTMzVXxnw@mail.gmail.com>
Date:	Thu, 23 Jun 2011 07:19:06 +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 Wed, Jun 22, 2011 at 11:03 PM, Andrea Arcangeli <aarcange@...hat.com> wrote:
> On Tue, Jun 21, 2011 at 09:32:39PM +0800, Nai Xia wrote:
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index d48ec60..b407a69 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -4674,6 +4674,7 @@ static int __init vmx_init(void)
>>               kvm_mmu_set_mask_ptes(0ull, 0ull, 0ull, 0ull,
>>                               VMX_EPT_EXECUTABLE_MASK);
>>               kvm_enable_tdp();
>> +             kvm_dirty_update = 0;
>>       } else
>>               kvm_disable_tdp();
>>
>
> Why not return !shadow_dirty_mask instead of adding a new var?
>
>>  struct mmu_notifier_ops {
>> +     int (*dirty_update)(struct mmu_notifier *mn,
>> +                          struct mm_struct *mm);
>> +
>
> Needs some docu.
>
> I think dirty_update isn't self explanatory name. I think
> "has_test_and_clear_dirty" would be better.
>
> If we don't flush the smp tlb don't we risk that we'll insert pages in
> the unstable tree that are volatile just because the dirty bit didn't
> get set again on the spte?
>
> The first patch I guess it's a sign of hugetlbfs going a little over
> the edge in trying to mix with the core VM... Passing that parameter
> &need_pte_unmap all over the place not so nice, maybe it'd be possible
> to fix within hugetlbfs to use a different method to walk the hugetlb
> vmas. I'd prefer that if possible.

OK, I'll have a try over other workarounds.
I am not feeling good about need_pte_unmap myself. :-)

Thanks for viewing!

-Nai

>
> Thanks,
> Andrea
>
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