linux-kernel - Re: [PATCH v2 2/2] mm: don't use compound_head() in virt_to_head

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Date:	Thu, 15 Jan 2015 21:30:12 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Jesper Dangaard Brouer <brouer@...hat.com>,
	rostedt@...dmis.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2 2/2] mm: don't use compound_head() in
 virt_to_head_page()

On Thu, 15 Jan 2015, Andrew Morton wrote:

> And perhaps some explanation here as to why virt_to_head_page() can
> safely use compound_head_fast().  There's an assumption here that
> nobody will be dismantling the compound page while virt_to_head_page()
> is in progress, yes?  And this assumption also holds for the calling
> code, because otherwise the virt_to_head_page() return value is kinda
> meaningless.

I think this assumption is pretty natural to make. A coupound_head that
works well while dismantling a compound page should be marked specially
and Joonsoo's definition should be the standard.


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