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

Christoph Lameter
2007-03-16T20:49:05Z

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.