linux-kernel - Re: [PATCH -mm v8 5/7] mmu-notifier: add clear

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Message-ID: <55A796E6.3090603@redhat.com>
Date:	Thu, 16 Jul 2015 13:35:02 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Andres Lagar-Cavilla <andreslc@...gle.com>,
	Vladimir Davydov <vdavydov@...allels.com>, kvm@...r.kernel.org,
	Eric Northup <digitaleric@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Minchan Kim <minchan@...nel.org>,
	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>,
	Greg Thelen <gthelen@...gle.com>,
	Michel Lespinasse <walken@...gle.com>,
	David Rientjes <rientjes@...gle.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Jonathan Corbet <corbet@....net>, linux-api@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-mm@...ck.org,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -mm v8 5/7] mmu-notifier: add clear_young callback



On 15/07/2015 21:16, Andres Lagar-Cavilla wrote:
>> > +static int kvm_mmu_notifier_clear_young(struct mmu_notifier *mn,
>> > +                                       struct mm_struct *mm,
>> > +                                       unsigned long start,
>> > +                                       unsigned long end)
>> > +{
>> > +       struct kvm *kvm = mmu_notifier_to_kvm(mn);
>> > +       int young, idx;
> For reclaim, the clear_flush_young notifier may blow up the secondary
> pte to estimate the access pattern, depending on hardware support (EPT
> access bits available in Haswell onwards, not sure about AMD, PPC,
> etc).

It seems like this problem is limited to pre-Haswell EPT.

I'm okay with the patch.  If we find problems later we can always add a
parameter to kvm_age_hva so that it effectively doesn't do anything on
clear_young.

Acked-by: Paolo Bonzini <pbonzini@...hat.com>

Paolo
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