linux-kernel - Re: [PATCH] mm: Save soft-dirty bits on file pages

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Date:	Mon, 29 Jul 2013 20:28:54 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Cyrill Gorcunov <gorcunov@...il.com>,
	Pavel Emelyanov <xemul@...allels.com>
Cc:	Linux MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
	Andy Lutomirski <luto@...capital.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Matt Mackall <mpm@...enic.com>,
	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>
Subject: Re: [PATCH] mm: Save soft-dirty bits on file pages

Cyrill Gorcunov <gorcunov@...il.com> writes:

> On Mon, Jul 29, 2013 at 06:08:55PM +0400, Pavel Emelyanov wrote:
>> >  
>> > -	if (!pte_none(*pte))
>> > +	ptfile = pgoff_to_pte(pgoff);
>> > +
>> > +	if (!pte_none(*pte)) {
>> > +#ifdef CONFIG_MEM_SOFT_DIRTY
>> > +		if (pte_present(*pte) &&
>> > +		    pte_soft_dirty(*pte))
>> 
>> I think there's no need in wrapping every such if () inside #ifdef CONFIG_...,
>> since the pte_soft_dirty() routine itself would be 0 for non-soft-dirty case
>> and compiler would optimize this code out.
>
> If only I'm not missing something obvious, this code compiles not only on x86,
> CONFIG_MEM_SOFT_DIRTY depends on x86 (otherwise I'll have to implement
> pte_soft_dirty for all archs).

why not

#ifndef pte_soft_dirty 
#define pte_soft_dirty(pte) 0 
#endif

and on x86 
#define pte_soft_dirty pte_soft_dirty

-aneesh

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