Re: [PATCH] rmap 13a

William Lee Irwin III
2002-05-07T18:03:28Z

On Mon, May 06, 2002 at 11:17:26PM -0300, Rik van Riel wrote:
>> rmap 13a:
>> - NUMA changes for page_address (Samuel Ortiz)

On Tue, May 07, 2002 at 06:37:41PM +0100, Christoph Hellwig wrote:
> I don't think the changes makes sense. If calculating page_address is
> complicated and slow enough to place it out-of-lin using page->virtual
> is much better.

On Tue, May 07, 2002 at 06:37:41PM +0100, Christoph Hellwig wrote:
> I'd suggest backing this patch out and instead always maintain page->virtual
> for discontigmem. While at this as a little cleanup you might want to
> define WANT_PAGE_VIRTUAL based on CONFIG_HIGHMEM || CONFIG_DISCONTIGMEM
> at the top of mm.h instead of cluttering it up.
> Christoph

This is a time/space tradeoff that may not necessarily be the case for
all discontiguous memory architectures. It seems to be so for SGI's
machines, though. I advocated this as a matter of generality, despite
not having a specific example of a machine that wants it. It's not
difficult to produce examples of small-memory architectures with
discontiguous memory, though SGI's discontigmem implementation does
not appear to be in widespread use for them.

Cheers,
Bill