Re: Reduce struct page by 8 bytes on 64bit

From: Jakub Jelinek (jakub@redhat.com)
Date: Wed Apr 16 2003 - 08:22:03 EST


On Wed, Apr 16, 2003 at 05:45:21AM -0700, David S. Miller wrote:
> From: Andi Kleen <ak@muc.de>
> Date: Tue, 15 Apr 2003 13:24:30 +0200
>
> I worked around this by declaring a new data type atomic_bitmask32
> with matching set_bit32/clear_bit32 etc. interfaces. Currently only
> on x86-64 aomitc_bitmask32 is defined to unsigned, everybody else
> still uses unsigned long. The other 64bit architectures can define it to
> unsigned too if they can confirm that it's ok to do.
>
> I have no problem with this.
>
> If you are clever, you can define a generic version even for the
> "unsigned long" 64-bit platforms. It's left as an exercise to
> the reader :-)

Why is any new macro needed?

struct page
{
#if BITS_PER_LONG == 64 && defined __BIG_ENDIAN
  union {
    unsigned long flags;
    atomic_t count;
  };
#elif BITS_PER_LONG == 64 && defined __LITTLE_ENDIAN
  union {
    unsigned long flags;
    struct {
      int : 32;
      atomic_t count;
    };
  };
#else
  unsigned long flags;
  atomic_t count;
#endif
...
};

should do the job.

        Jakub
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