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

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Message-ID: <Pine.LNX.4.64.0703161346060.6204@schroedinger.engr.sgi.com>
Date:	Fri, 16 Mar 2007 13:48:58 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Martin Bligh <mbligh@...igh.org>
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

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.

> 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.

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