linux-kernel - Re: [PATCH 6/6] KVM: MMU: Avoid handling same rmap_pde in kvm_handle_hva

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Message-Id: <20120701221857.f3b9ee04e590ff7f1a0a335a@gmail.com>
Date:	Sun, 1 Jul 2012 22:18:57 +0900
From:	Takuya Yoshikawa <takuya.yoshikawa@...il.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	Takuya Yoshikawa <yoshikawa.takuya@....ntt.co.jp>,
	mtosatti@...hat.com, agraf@...e.de, paulus@...ba.org,
	aarcange@...hat.com, kvm@...r.kernel.org, kvm-ppc@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/6] KVM: MMU: Avoid handling same rmap_pde in
 kvm_handle_hva_range()

On Sun, 01 Jul 2012 10:41:05 +0300
Avi Kivity <avi@...hat.com> wrote:

> >> > Note: in the new code we could not use trace_kvm_age_page(), so we just
> >> > dropped the point from kvm_handle_hva_range().
> >> > 
> >> 
> >> Can't it be pushed to handler()?
> > 
> > Yes, but it will be changed to print rmap, not hva and gfn.
> > I will do in the next version.
> 
> We should try to avoid changing the tracepoint ABI.  If we pass the
> memslot to handler(), we should be able to reconstruct the gfn and hva.

That's not enough because we only know rmapp in the handler: we also need
level or something.  I agree that passing memslot for keeping the ABI is
good, but how about two more arguments?

BTW, trace_kvm_age_page() is tracing every handler, not just kvm_age_rmapp().
Is this intentional?

If we trace in the caller, in kvm_age_hva(), we know hva, but not gfn.

Thanks,
	Takuya
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