Re: [patch] CONFIG_ARCH_HAS_ATOMIC_UNSIGNED

[Dave Hansen <haveblue@us.ibm.com>]

On Thu, 2004-12-16 at 22:11, Andi Kleen wrote:
> On Thu, Dec 16, 2004 at 04:44:20PM -0800, Dave Hansen wrote:
> > This reduces another one of the dependencies that struct page's
> > definition has on any arch-specific header files.  Currently,
> > only x86_64 uses this, so it's the only architecture that needed
> > to be modified.
> 
> That's for page_flags_t, right?

Yep.

> I think it could be dropped right now and just use unsigned long for
> flags again. 

That's fine with me (and a much simpler patch).

> Since the objrmap work the saved 4 bytes in struct page are wasted in padding 
> and I haven't found a way to use them for real space saving again
> because all other members are 8 byte or paired 4 byte.

Well, since you asked... :)

In a newer revision of the nonlinear code, Andy Whitcroft has decided to
store part of the page_to_pfn() translation directly in page->flags,
right next to the zone information.  This is a bit of a squeeze on
32-bit arches, but on the 64-bit ones, there's plenty of room since
nobody is using the upper 32 bits at all.

I didn't realize that x86_64 had a 32-bit type there, so we probably
would have suggested turning it into a 64-bit one eventually.

-- Dave

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