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

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Date:	Tue, 20 Dec 2011 13:10:41 -0500
From:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:	Wu Fengguang <fengguang.wu@...el.com>
CC:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	"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 11:35:37AM +0800, Wu Fengguang wrote:
> 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.

Yes, both of KPF_COMPOUND_HEAD/TAIL flags are automatically set for thp.
So above patch description was wrong and should be fixed.
(I didn't notice that because page-types hid compound_head/tail flags
without --raw flag. Sorry for confusion.)

> > Signed-off-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
> 
> Reviewed-by: Wu Fengguang <fengguang.wu@...el.com>

Thank you.

Naoya
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