linux-kernel - Re: DRM lock ordering fix series

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Message-ID: <49CDE401.2020502@inria.fr>
Date:	Sat, 28 Mar 2009 09:46:57 +0100
From:	Brice Goglin <Brice.Goglin@...ia.fr>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Eric Anholt <eric@...olt.net>, Andi Kleen <andi@...stfloor.org>,
	linux-kernel@...r.kernel.org, dri-devel@...ts.sourceforge.net,
	Nick Piggin <nickpiggin@...oo.com.au>
Subject: Re: DRM lock ordering fix series

Peter Zijlstra wrote:
> Also note that doing large gup() with gup_fast() will be undesirable due
> to it disabling IRQs. So iterating say several MB worth of pages will
> hurt like crazy. Currently all gup_fast() users do a single page lookup.
>   

In 2.6.29, fs/bio.c:955, fs/direct-io.c:153 and fs/splice.c:1222 do
multiple-pages lookup at once. The latter might be limited to 16 pages
because of the pipe-depth, I don't know about the formers.

Is there some sort of reasonable limit? A couple dozens pages at once maybe?

Brice

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