Re: Creating a per-task kernel space for kmap, user pagetables, et al

Christoph Hellwig
2002-03-20T20:35:57Z

On Wed, Mar 20, 2002 at 09:23:41PM +0100, Andrea Arcangeli wrote:
> we need to walk pagetables not just from the current task and mapping
> pagetables there would decrase the user address space too much.

Who sais it should be taken from user address space?
For example openunix takes a small (I think 4MB) part of the normal KVA
to be per-process mapped.

> I think you're missing the problem with mainline. There is no shortage
> of virtual address space, there is a shortage of physical ram in the
> zone normal. So we cannot keep them in zone normal (and there's no such
> thing as "mapping in zone_normal"). Maybe I misunderstood what you were
> saying.

The problem is not the 4GB ZONE_NORMAL but the ~1GB KVA space.
UnixWare/OpenUnix had huge problems getting all kernel structs for managing
16GB virtual into that - on the other hand their struct page is more
then twice as big as ours..