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Date: Mon, 2 Aug 2010 10:48:46 -0500 (CDT)
From: Christoph Lameter <cl@linux-foundation.org>
Subject: Re: [PATCH] Tight check of pfn_valid on sparsemem - v4
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To: Russell King - ARM Linux <linux@arm.linux.org.uk>
Cc: Dave Hansen <dave@linux.vnet.ibm.com>, Minchan Kim <minchan.kim@gmail.com>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>, Milton Miller <miltonm@bga.com>, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>, Mel Gorman <mel@csn.ul.ie>, Johannes Weiner <hannes@cmpxchg.org>, Kukjin Kim <kgene.kim@samsung.com>
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On Sat, 31 Jul 2010, Russell King - ARM Linux wrote:

> Looking at vmemmap sparsemem, we need to fix it as the page table
> allocation in there bypasses the arch defined page table setup.

You are required to define your own vmemmap_populate function. In that you
can call some of the provided functions or use your own.

> This causes a problem if you have 256-entry L2 page tables with no
> room for the additional Linux VM PTE support bits (such as young,
> dirty, etc), and need to glue two 256-entry L2 hardware page tables
> plus a Linux version to store its accounting in each page.  See
> arch/arm/include/asm/pgalloc.h.
>
> So this causes a problem with vmemmap:
>
>                 pte_t entry;
>                 void *p = vmemmap_alloc_block_buf(PAGE_SIZE, node);
>                 if (!p)
>                         return NULL;
>                 entry = pfn_pte(__pa(p) >> PAGE_SHIFT, PAGE_KERNEL);
>
> Are you willing for this stuff to be replaced by architectures as
> necessary?

Sure its designed that way. If we missed anything we'd surely add it.

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