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

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Message-ID: <Pine.LNX.4.64.0802071530040.3845@schroedinger.engr.sgi.com>
Date:	Thu, 7 Feb 2008 15:32:29 -0800 (PST)
From:	Christoph Lameter <clameter@....com>
To:	Vegard Nossum <vegard.nossum@...il.com>
cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Andi Kleen <andi@...stfloor.org>,
	Richard Knutsson <ricknu-0@...dent.ltu.se>
Subject: Re: [PATCH 1/2] kmemcheck v3

On Fri, 8 Feb 2008, Vegard Nossum wrote:

> The tracking that kmemcheck does is actually a byte-for-byte tracking
> of whether memory has been initialized or not. Think of it as valgrind
> for the kernel. We do this by "hiding" pages (marking them non-present
> for for MMU) and taking the page faults, which effectively tells us
> what memory is being attempted to be read from or written to.

Ahh. Okay. But ZONE_DMA pages are exempt from that scheme? You know 
that ZONE_NORMAL pages can undergo dma?

> I chose to implement this in the slab layer because this is probably
> where most of the interesting allocations are coming from, and this
> gives us a better control over what most users/callers care about,
> namely the specific objects.

But the slab layer allocates pages < PAGE_SIZE. You need to take a fault 
right? So each object would need its own page?
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