linux-kernel - Re: [patch 1/2] x86: track memtype for RAM in page struct

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Message-ID: <20080914141230.GB17727@elte.hu>
Date:	Sun, 14 Sep 2008 16:12:30 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>
Cc:	arjan@...ux.intel.com, tglx@...utronix.de, hpa@...or.com,
	andi@...stfloor.org, linux-kernel@...r.kernel.org,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [patch 1/2] x86: track memtype for RAM in page struct


* Venkatesh Pallipadi <venkatesh.pallipadi@...el.com> wrote:

> From: Suresh Siddha <suresh.b.siddha@...el.com>
> Subject: [patch 1/2] x86: track memtype for RAM in page struct
> 
> Track the memtype for RAM pages in page struct instead of using the 
> memtype list. This avoids the explosion in the number of entries in 
> memtype list (of the order of 20,000 with AGP) and makes the PAT 
> tracking simpler. We are using PG_arch_1 bit in page->flags.

this is in contradiction to this comment:

>  /*
> + * RED-PEN:  TODO: Add PageReserved() check aswell here,
> + * once we add SetPageReserved() to all the drivers using
> + * set_memory_* or set_pages_*

if it's marked PG_arch_1, why is there any need for PageReserved?

> + *
> + * This will help prevent accidentally freeing pages
> + * before setting the attribute back to WB.

setting it PageReserved is a hack. We should set it PG_arch_1 and extend 
the page allocator to emit a kernel warning if a PG_arch_1 page is 
freed.

	Ingo
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