linux-kernel - Re: [PATCH 00/18] Make common x86 arch area for i386 and x86_64

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Date:	Fri, 16 Mar 2007 13:59:52 -0700
From:	Martin Bligh <mbligh@...igh.org>
To:	Christoph Lameter <clameter@....com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Chris Wright <chrisw@...s-sol.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Glauber de Oliveira Costa <glommer@...il.com>,
	Andy Whitcroft <apw@...dowen.org>
Subject: Re: [PATCH 00/18] Make common x86 arch area for i386 and x86_64 -
 Take 2

Christoph Lameter wrote:
> On Fri, 16 Mar 2007, Martin Bligh wrote:
> 
>> You have to do some sort of lookup anyway, and Andy seemed to have them
>> all folded into one.
> 
> What lookup would you need to do? On x86_64 even the TLB use is 
> hidden by the existing 2M entries for 1-1 mappings.
> 
>> Or are you trying to avoid this by going to back to the crud we had
>> in 2.4 where we pretend mem_map is one big array, indexed by pfn with
>> huge sparsely mapped holes in it?
> 
> Yes that the advanced way of doing it rather than adding useless custom 
> lookups.

For starters, you can't do that sparse a mapping on a 32 bit system.
I'll let Andy explain the rest of it.

>> Would be nice to work out (and document somewhere) what the pros and
>> cons of virtual memmap vs sparsemem were - ISTR one of the arguments
>> was extremely sparsely layed out machines, and you needed sparsemem
>> for that. But right now we have 3 solutions, which is not a good
>> situation.
> 
> Please read my posts to linux-mm on that subject. We discussed it last 
> year in detail and the agreement was that the sparsemem crud needs to be 
> taken out. Kame-san posted patches to do that.

"the agreement"? So Andy agreed to taking it out? Or you and Kame did?

M.


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