linux-kernel - Re: [PATCH] pagemap: fix wrong KPF

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Date:	Tue, 25 Sep 2012 17:20:48 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi.kleen@...el.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pagemap: fix wrong KPF_THP on slab pages

On Tue, 25 Sep 2012, Naoya Horiguchi wrote:

> KPF_THP can be set on non-huge compound pages like slab pages, because
> PageTransCompound only sees PG_head and PG_tail. Obviously this is a bug
> and breaks user space applications which look for thp via /proc/kpageflags.
> Currently thp is constructed only on anonymous pages, so this patch makes
> KPF_THP be set when both of PageAnon and PageTransCompound are true.
> 
> Changelog in v2:
>   - add a comment in code
> 
> Signed-off-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>

Wouldn't PageTransCompound(page) && !PageHuge(page) && !PageSlab(page) be 
better for a future extension of thp support?
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