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

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Message-ID: <51F67B27.9040004@parallels.com>
Date:	Mon, 29 Jul 2013 18:24:39 +0400
From:	Pavel Emelyanov <xemul@...allels.com>
To:	Cyrill Gorcunov <gorcunov@...il.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

On 07/29/2013 06:14 PM, Cyrill Gorcunov wrote:
> 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).

For non-x86 case there are stubs in include/asm-generic/pgtable.h that would
act as if the CONFIG_MEM_SOFT_DIRTY is off.

Thanks,
Pavel
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