linux-kernel - Re: [PATCH 1/2] kmemcheck v3

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Message-ID: <84144f020802072348p2f9bda73m52fcc07e272dd68c@mail.gmail.com>
Date:	Fri, 8 Feb 2008 09:48:58 +0200
From:	"Pekka Enberg" <penberg@...helsinki.fi>
To:	"Christoph Lameter" <clameter@....com>
Cc:	"Vegard Nossum" <vegard.nossum@...il.com>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	"Ingo Molnar" <mingo@...e.hu>, "Andi Kleen" <andi@...stfloor.org>,
	"Richard Knutsson" <ricknu-0@...dent.ltu.se>
Subject: Re: [PATCH 1/2] kmemcheck v3

Hi Christoph,

On Thu, 7 Feb 2008, Vegard Nossum wrote:
> > - DMA can be a problem since there's generally no way for kmemcheck to
> >   determine when/if a chunk of memory is used for DMA. Ideally, DMA should be
> >   allocated with untracked caches, but this requires annotation of the
> >   drivers in question.

On Feb 8, 2008 9:10 AM, Christoph Lameter <clameter@....com> wrote:
> There is a fundamental misunderstanding here: GFP_DMA allocations have
> nothing to do with DMA. Rather GFP_DMA means allocate memory in a special
> range of physical memory that is required by legacy devices that cannot
> use the high address bits for one or the other reason. Any regular
> memory can be used for DMA.

No there isn't and we've been over this with Vegard many times :-).
Christoph, can you actually see this in the patch? There shouldn't be
any __GFP_DMA confusion there. What we have is per-object
__GFP_NOTRACK which can be used to suppress false positives for
DMA-filled objects and SLAB_NOTRACK for whole _caches_ that contains
objects which we must not take page faults at all.
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