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

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Date:	Mon, 2 Aug 2010 10:48:46 -0500 (CDT)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
cc:	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Minchan Kim <minchan.kim@...il.com>,
	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>,
	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 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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