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

From: Daniel Phillips (
Date: Thu May 02 2002 - 14:08:18 EST

On Thursday 02 May 2002 20:57, Andrea Arcangeli wrote:
> On Thu, May 02, 2002 at 12:31:52PM -0700, Martin J. Bligh wrote:
> > between physical to virtual memory to a non 1-1 mapping.
> correct. The direct mapping is nothing magic, it's like a big static
> kmap area. Everybody is required to use
> virt_to_page/page_address/pci_map_single/... to switch between virtual
> address and mem_map anyways (thanks to the discontigous mem_map), so you
> can use this property by making discontigous the virtual space as well,
> not only the mem_map. discontigmem basically just allows that.

And what if you don't have enough virtual space to fit all the memory you
need, plus the holes? Config_nonlinear handles that, config_discontig

> > No, you don't need to call changing that mapping "CONFIG_NONLINEAR",
> > but that's basically what the bulk of Dan's patch does, so I think we should
> > steal it with impunity ;-)
> The difference is that if you use discontigmem you don't clobber the
> common code in any way,

First that's wrong. Look at _alloc_pages and tell me that config_discontig
doesn't impact the common code (in fact, it adds two extra subroutine
calls, including two loops, to every alloc_pages call).

Secondly, config_nonlinear does not clobber the common code. If it does,
please show me where.

When config_nonlinear is not enabled, suitable stubs are provided to make it

> Actually the same mmu technique can be used to coalesce in virtual
> memory the discontigous chunks of iSeries, then you left the lookup in
> the tree to resolve from mem_map to the right virtual address and from
> the right virtual address back to mem_map. (and you left DISCONTIGMEM
> disabled) I think it should be possible.

So you're proposing a new patch? Have you chosen a name for it? How
about 'config_nonlinear'? ;-)

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