linux-kernel - Re: [PATCH 02/11] Add "handle page fault" PV helper.

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Message-ID: <20091102160410.GF27911@redhat.com>
Date:	Mon, 2 Nov 2009 18:04:10 +0200
From:	Gleb Natapov <gleb@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	kvm@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 02/11] Add "handle page fault" PV helper.

On Mon, Nov 02, 2009 at 10:22:14AM +0100, Ingo Molnar wrote:
> 
> * Gleb Natapov <gleb@...hat.com> wrote:
> 
> > diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> > index f4cee90..14707dc 100644
> > --- a/arch/x86/mm/fault.c
> > +++ b/arch/x86/mm/fault.c
> > @@ -952,6 +952,9 @@ do_page_fault(struct pt_regs *regs, unsigned long error_code)
> >  	int write;
> >  	int fault;
> >  
> > +	if (arch_handle_page_fault(regs, error_code))
> > +		return;
> > +
> 
> This patch is not acceptable unless it's done cleaner. Currently we 
> already have 3 callbacks in do_page_fault() (kmemcheck, mmiotrace, 
> notifier), and this adds a fourth one. Please consolidate them into a 
> single callback site, this is a hotpath on x86.
> 
This call is patched out by paravirt patching mechanism so overhead should be
zero for non paravirt cases. What do you want to achieve by consolidate
them into single callback? I mean the code will still exist and will have to be
executed on every #PF. Is the goal to move them out of line? 

> And please always Cc: the x86 maintainers to patches that touch x86 
> code.
> 
Will do.

--
			Gleb.
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