debugobjects: Add percpu free pools

When a multi-threaded workload does a lot of small memory object
allocations and deallocations, it may cause the allocation and freeing of
many debug objects. This will make the global pool_lock a bottleneck in the
performance of the workload.  Since interrupts are disabled when acquiring
the pool_lock, it may even cause hard lockups to happen.

To reduce contention of the global pool_lock, add a percpu debug object
free pool that can be used to buffer some of the debug object allocation
and freeing requests without acquiring the pool_lock.  Each CPU will now
have a percpu free pool that can hold up to a maximum of 64 debug
objects. Allocation and freeing requests will go to the percpu free pool
first. If that fails, the pool_lock will be taken and the global free pool
will be used.

The presence or absence of obj_cache is used as a marker to see if the
percpu cache should be used.

Signed-off-by: Waiman Long <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Yang Shi <[email protected]>
Cc: "Joel Fernandes (Google)" <[email protected]>
Cc: Qian Cai <[email protected]>
Cc: Zhong Jiang <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

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