Re: Bug: Discontigmem virt_to_page() [Alpha,ARM,Mips64?]

From: Andrea Arcangeli (
Date: Thu May 02 2002 - 08:34:02 EST

On Wed, May 01, 2002 at 04:41:17AM +0200, Daniel Phillips wrote:
> On Thursday 02 May 2002 03:43, Andrea Arcangeli wrote:
> > On Wed, May 01, 2002 at 03:26:22AM +0200, Daniel Phillips wrote:
> > > For your information, the mem_map lives in *virtual* memory, it does not
> > > need to change location, only the kernel page tables need to be updated,
> > > to allow a section of kernel memory to be moved to a different physical
> > > location. For user memory, this was always possible, now it is possible
> > > for kernel memory as well. Naturally, it's not all you have to do to get
> > > hotplug memory, but it's a big step in that direction.
> >
> > what kernel pagetables?
> The normal page tables that are used to map kernel memory.
> > pagetables for space that you left free for what?
> These page tables have not been left free for anything. The nice thing about
> page tables is that you can change the page table entries to point wherever
> you want. (I know you know this.) This is what config_nonlinear supports,
> and that is why it's called config_nonlinear. When we want to remap part of
> the kernel memory to a different piece of physical memory, we just need to
> fill in some pte's. The tricky part is knowing how to fill in the ptes, and
> config_nonlinear takes care of that.
> > You waste virtual space for that at the very least on x86 that is
> > just very tigh, at this point kernel virtual space is more costly than
> > physical space these days. And nevertheless most archs doesn't have
> > pagetables at all to read and write the page structures. yes it's
> > virtual memory but it's a direct mapping.
> Most architectures? That's quite possibly an exaggeration. Some
> architectures - MIPS32 for example - make this difficult or impossible,
> and so what? Those can't do software hotplug memory, sorry.

alpha is the same as mips I think. sparc would be the same too if
there's any discontigmem sparc. Dunno of arm. We're talking about
architectures needing discontigmem, 99% percent of users doesn't need
discontigmem in the first place, you never need discontigmem in x86 and
even in new-numa you don't need discontigmem, you want to pass through
discontigmem only to get the numa topology description that the current
discontigmem provides via the pgdat.

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

This archive was generated by hypermail 2b29 : Tue May 07 2002 - 22:00:13 EST