Re: [PATCH] rmap 13a

William Lee Irwin III
2002-05-08T11:13:49Z

On Wed, May 08, 2002 at 04:06:58AM -0700, Samuel Ortiz wrote:
> 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.

Also, to be perfectly clear despite my message of perhaps extreme
conservatism regarding space conservation, I believe the time/space
tradeoff is an architectural consideration. Though I specifically
requested that a calculated UNMAP_NR_DENSE() be implemented, I by no
means oppose the usage of page->virtual for those architectures where
demonstrable performance benefits arise from the additional space
consumption of the extra field.

Cheers,
Bill