Re: Reduce struct page by 8 bytes on 64bit

[Andi Kleen <ak@muc.de>]

On Wed, Apr 16, 2003 at 04:38:14PM +0200, David S. Miller wrote:
>    From: Andi Kleen <ak@muc.de>
>    Date: Wed, 16 Apr 2003 16:43:12 +0200
>    
>    On sparc64. But is that true too for all other 64bit architectures supported?
>    
>    e.g. How about PA-RISC? (always seems to do things differently)
>    
> It cannot require more than the existing API requires, which is
> "unsigned long *bitmask", ie. anything equivalent in behavior to an
> unsigned long pointer is good enough.

Sure, but perhaps it does assume all accesses to this bitmap are going
through the set_bit functions. e.g. consider an implementation that
uses a spinlock for this - parisc seems to do that for example
from a quick look into their bitops.h. And they have an 64bit kernel
too.

In this case part of the unsigned long could be accessed directly 
using the aliasing.

-Andi