On 08/12/2013 04:43 PM, Yinghai Lu wrote:

quoted

quoted

commit 8170e6bed465b4b0c7687f93e9948aca4358a33b
Author: H. Peter Anvin [off-list ref]
Date:   Thu Jan 24 12:19:52 2013 -0800

    x86, 64bit: Use a #PF handler to materialize early mappings on demand

Before that, we have maping from [0,512M) in head_64.S, and we can
spare two pages [0-1M).  After that change, we can not reuse pages anymore.

When we have more than 512M ram, we need extra page for pgd page with
[512G, 1024g).

Increase pages in BRK for page table to solve the booting problem.

So how much does this get us up to?  1TB?  That's actually _fairly_
small today.  I've got a fairly old machine with that much in it, and
it's only half full of DIMMs.

It's also a bit worrying that this is completely disconnected from the
other code in the kernel that is concerned with the amount of total
address space in the system: MAX_PHYSADDR_BITS.