linux-kernel - Re: [RFC][PATCH 2/3] pagemap: export KPF

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Date:	Tue, 20 Dec 2011 11:35:37 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Andi Kleen <andi@...stfloor.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH 2/3] pagemap: export KPF_THP

On Tue, Dec 20, 2011 at 02:38:38AM +0800, Naoya Horiguchi wrote:
> This flag shows that a given pages is a subpage of transparent hugepage.
> It does not care about whether it is a head page or a tail page, because
> it's clear from pfn of the target page which you should know when you read
> /proc/kpageflags.

OK, this is aligning with KPF_HUGE. For those who only care about
head/tail pages, will the KPF_COMPOUND_HEAD/KPF_COMPOUND_TAIL flags be
set automatically for thp? Which may be more convenient to test/filter
than the page address.

> Signed-off-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>

Reviewed-by: Wu Fengguang <fengguang.wu@...el.com>

As you already discussed, the below #ifdef should be removed.
In fact, kernel-page-flags.h is intended for direct inclusion by
user space tools, so must not have any conditional defines.

> --- 3.2-rc5.orig/include/linux/kernel-page-flags.h
> +++ 3.2-rc5/include/linux/kernel-page-flags.h
> @@ -31,6 +31,10 @@
>  
>  #define KPF_KSM			21
>  
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +#define KPF_THP			22
> +#endif
> +
>  /* kernel hacking assistances
>   * WARNING: subject to change, never rely on them!
>   */
> -- 
> 1.7.7.3
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