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Re: sparsemem support for mips with highmem

To: David VomLehn <dvomlehn@cisco.com>
Subject: Re: sparsemem support for mips with highmem
From: Christoph Lameter <cl@linux-foundation.org>
Date: Tue, 19 Aug 2008 08:06:21 -0500
Cc: Randy Dunlap <rdunlap@xenotime.net>, C Michael Sundius <Michael.sundius@sciatl.com>, Dave Hansen <dave@linux.vnet.ibm.com>, Thomas Bogendoerfer <tsbogend@alpha.franken.de>, linux-mm@kvack.org, linux-mips@linux-mips.org, jfraser@broadcom.com, Andy Whitcroft <apw@shadowen.org>
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David VomLehn wrote:

> On MIPS processors, the kernel runs in unmapped memory, i.e. the TLB
> isn't even
> used, so I don't think you can use that trick. So, this comment doesn't
> apply to
> all processors.

In that case you have a choice between the overhead of sparsemem lookups in
every pfn_to_page or using TLB entries to create a virtually mapped memmap
which may create TLB pressure.

The virtually mapped memmap results in smaller code and is typically more
effective since the processor caches the TLB entries.



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