slub: RFC lockless allocation paths V1

Draft of a patchset to make the allocation paths lockless as well.

I have done just a hackbench test on this to make sure that it works. Various additional overhead is added to the fastpaths so this may require additional work before it becomes mergeable.

The first two patches are cleanup patches that have been posted a couple of times. Those can be merged.

The basic principle is to use double word atomic allocations to check lists of objects in and out of the per cpu structures and the per page structures.

Since we can only handle two words atomically we need to reduce the state being kept for per cpu queues. Thus the page and the node field in kmem_cache_cpu have to be dropped. Both of those values can be determined from an object pointer after all but the calculation of those values impacts the performance of the allocator. Not sure what the impact is. Could be offset by the removal of the overhead for interrupt disabling/enabling and the code savings because the per cpu state for queueing is much less.

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