linux-kernel - Re: [PATCH] Tight check of pfn_valid on sparsemem

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Message-ID: <20100728225756.GA6108@barrios-desktop>
Date:	Thu, 29 Jul 2010 07:57:56 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Milton Miller <miltonm@....com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	Russell King <linux@....linux.org.uk>,
	Mel Gorman <mel@....ul.ie>,
	Johannes Weiner <hannes@...xchg.org>,
	Kukjin Kim <kgene.kim@...sung.com>
Subject: Re: [PATCH] Tight check of pfn_valid on sparsemem - v4

On Wed, Jul 28, 2010 at 12:02:16PM -0500, Christoph Lameter wrote:
> On Thu, 29 Jul 2010, Minchan Kim wrote:
> > invalid memmap pages will be freed by free_memmap and will be used
> > on any place. How do we make sure it has PG_reserved?
> 
> Not present memmap pages make pfn_valid fail already since there is no
> entry for the page table (vmemmap) or blocks are missing in the sparsemem
> tables.
> 
> > Maybe I don't understand your point.
> 
> I thought we are worrying about holes in the memmap blocks containing page
> structs. Some page structs point to valid pages and some are not. The
> invalid page structs need to be marked consistently to allow the check.

The thing is that memmap pages which contains struct page array on hole will be 
freed by free_memmap in ARM. Please loot at arch/arm/mm/init.c.
And it will be used by page allocator as free pages.

-- 
Kind regards,
Minchan Kim
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