Le vendredi 29 juillet 2011 A  16:18 -0700, Andi Kleen a A(C)crit :

Christoph Lameter [off-list ref] writes:

quoted

On Fri, 29 Jul 2011, Pekka Enberg wrote:

quoted

We haven't come up with a solution to keep struct page size the same but I
think it's a reasonable trade-off.

The change requires the page struct to be aligned to a double word
boundary. 

Why is that?

Because cmpxchg16b is believed to require a 16bytes alignment.

http://siyobik.info/main/reference/instruction/CMPXCHG8B%2FCMPXCHG16B

64-Bit Mode Exceptions
...

#GP(0) 	If the memory address is in a non-canonical form. If memory
operand for CMPXCHG16B is not aligned on a 16-byte boundary. If
CPUID.01H:ECX.CMPXCHG16B[bit 13] = 0.



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