linux-kernel - Re: [PATCH] Document huge memory/cache overhead of memory controller in Kconfig

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Message-ID: <47BD1052.2090204@linux.vnet.ibm.com>
Date:	Thu, 21 Feb 2008 11:16:58 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Nick Piggin <nickpiggin@...oo.com.au>
CC:	Andi Kleen <andi@...stfloor.org>, akpm@...l.org, torvalds@...l.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] Document huge memory/cache overhead of memory controller
 in Kconfig

Nick Piggin wrote:
>> 1. We could create something similar to mem_map, we would need to handle 4
> 
>> different ways of creating mem_map.
> 
>> 2. On x86 with 64 GB ram, if we decided to use vmalloc space, we would need
> 
>> 64 MB of vmalloc'ed memory
> 
> That's going to be a big job. You could probably do it quite easily for
> 
> flatmem (just store an offset into the start of your page array), and
> 
> maybe even sparsemem (add some "extra" information to the extents).
> 
>> I have not explored your latest suggestion of pfn <-> memory controller
> 
>> mapping yet. I'll explore it and see how that goes.
> 
> If you did that using a radix-tree, then it could be a runtime option
> 
> without having to use vmalloc. And you wouldn't have to care about
> 
> memory models. I'd say it will be the fastest way to get a prototype
> 
> running.
> 

OK, I'll explore and prototype the radix tree based approach and see how that goes.

-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL
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