Re: [PATCH] rmap 13a

On Tue, 7 May 2002, Christoph Hellwig wrote:

On Mon, May 06, 2002 at 11:17:26PM -0300, Rik van Riel wrote:

quoted

rmap 13a:
  - NUMA changes for page_address                         (Samuel Ortiz)

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.

This is right for machines who don't care about the struct page size, like
SGI ones, and big NUMA machines in general.

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.

Some discontiguous architectures (ARM, for example) may be interested in
getting rid of page->virtual, and thus shrinking the struct page size.
So you may want to get the possibility of having
(!CONFIG_HIGHMEM)&&CONFIG_DISCONTIGMEM and not wanting page->virtual.
So, WANT_PAGE_VIRTUAL can not be defined with CONFIG_HIGHMEM ||
CONFIG_DISCONTIGMEM.
However, I should modify my patch in order for the changes to take place
only if (!CONFIG_HIGHMEM)&&(CONFIG_DISCONTIG_MEM)&&(!WANT_PAGE_VIRTUAL).
I can come back with the right changes if that makes sense to you.

Cheers,
Samuel.

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