linux-kernel - Re: [PATCH 08/40] autonuma: teach gup_fast about pte

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Message-ID: <4FEDC961.1060306@redhat.com>
Date:	Fri, 29 Jun 2012 11:27:29 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Andrea Arcangeli <aarcange@...hat.com>
CC:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Hillf Danton <dhillf@...il.com>, Dan Smith <danms@...ibm.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, Paul Turner <pjt@...gle.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Mike Galbraith <efault@....de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Bharata B Rao <bharata.rao@...il.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Johannes Weiner <hannes@...xchg.org>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Christoph Lameter <cl@...ux.com>,
	Alex Shi <alex.shi@...el.com>,
	Mauricio Faria de Oliveira <mauricfo@...ux.vnet.ibm.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Don Morris <don.morris@...com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [PATCH 08/40] autonuma: teach gup_fast about pte_numa

On 06/28/2012 08:55 AM, Andrea Arcangeli wrote:
> gup_fast will skip over non present ptes (pte_numa requires the pte to
> be non present). So no explicit check is needed for pte_numa in the
> pte case.
>
> gup_fast will also automatically skip over THP when the trans huge pmd
> is non present (pmd_numa requires the pmd to be non present).
>
> But for the special pmd mode scan of knuma_scand
> (/sys/kernel/mm/autonuma/knuma_scand/pmd == 1), the pmd may be of numa
> type (so non present too), the pte may be present. gup_pte_range
> wouldn't notice the pmd is of numa type. So to avoid losing a NUMA
> hinting page fault with gup_fast we need an explicit check for
> pmd_numa() here to be sure it will fault through gup ->
> handle_mm_fault.
>
> Signed-off-by: Andrea Arcangeli<aarcange@...hat.com>

Assuming pmd_numa will get the documentation I asked for a few
patches back, this patch is fine, since people will just be able
to look at a nice comment above pmd_numa and see what is going on.

Acked-by: Rik van Riel <riel@...hat.com>

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