Re: [PATCH 00/18] Make common x86 arch area for i386 and x86_64 - Take 2

Martin Bligh
2007-03-16T20:59:55Z

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.