[cpuops cmpxchg double V3 0/5] this_cpu_cmpxchg_double support

[Christoph Lameter]

This patch series introduces this_cpu_cmpxchg_double().

x86 cpus support cmpxchg16b and cmpxchg8b instuction which are capable of
switching two words instead of one during a cmpxchg.
Two words allow to swap more state in an atomic instruction.

this_cpu_cmpxchg_double() is used in the slub allocator to avoid
interrupt disable/enable in both alloc and free fastpath.
Using the new operation significantly speeds up the fastpaths.

V1->V2
	- Change parameter convention for this_cpu_cmpxchg_double. Specify both
	  percpu variables in same way as the two old and new values.
	- Do not require a per cpu pointer but a variable to conform to the
	  convention used in other this_cpu_ops.

V2->V3:
        - Do not use CONFIG_DEBUG_VM to enable cmpxchg diagnostics. Use
          custom SLUB define instead.
        - Add patch to move min_partial into a different cacheline.
        - Rediff

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