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

Christoph Lameter
2007-03-16T20:59:24Z

On Fri, 16 Mar 2007, David Miller wrote:

> From: Christoph Lameter <clameter@sgi.com>
> Date: Fri, 16 Mar 2007 13:52:18 -0700 (PDT)
>
> > Virtual mmap allows holes in the same way as page tables do.
>
> I don't want to take expensive TLB misses to lookup a page.

Ummm. You are missing key details please look at linux-mm. We will use
huge tlb entries for the mmap and its optional.

> TLB misses are extremely expensive on some platforms, that's why
> I try to make all the critical structures go through the 4MB
> locked TLB entry for the kernel image, or failing that the
> 4MB linear mappings at PAGE_OFFSET on sparc64.

Exactly. That is why 16M TLB entries speed up the kernel by
4-5% using vmmemmap on ia64. Basically we end up with one TLB per node
for the vmemmap which always stays in the cache. No additional lookups.
Without vmemmap we still need a 16M TLB for the 1-1 kernel mapping. This
jsut cuts out the crud from sparsemem.