Subject: Re: [PATCH -mm v8 5/7] mmu-notifier: add clear_young callback
To: Andres Lagar-Cavilla <andreslc@google.com>,
        Vladimir Davydov <vdavydov@parallels.com>, kvm@vger.kernel.org,
        Eric Northup <digitaleric@google.com>
References: <cover.1436967694.git.vdavydov@parallels.com>
 <82693bd5b5dbf4e65657fa22288942650aa04a0a.1436967694.git.vdavydov@parallels.com>
 <CAJu=L58yzBr8+XaV90x+S60YnJzd7Yr2fDEgaQ0bcCKpwzSAhw@mail.gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
        Minchan Kim <minchan@kernel.org>,
        Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>,
        Johannes Weiner <hannes@cmpxchg.org>, Michal Hocko <mhocko@suse.cz>,
        Greg Thelen <gthelen@google.com>,
        Michel Lespinasse <walken@google.com>,
        David Rientjes <rientjes@google.com>,
        Pavel Emelyanov <xemul@parallels.com>,
        Cyrill Gorcunov <gorcunov@openvz.org>,
        Jonathan Corbet <corbet@lwn.net>, linux-api@vger.kernel.org,
        linux-doc@vger.kernel.org, linux-mm@kvack.org, cgroups@vger.kernel.org,
        linux-kernel@vger.kernel.org
From: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <55A796E6.3090603@redhat.com>
Date: Thu, 16 Jul 2015 13:35:02 +0200
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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@redhat.com>

Paolo
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