SLUB with Queueing beats SLAB in hackbench

The following patchset cleans some pieces up and then equips SLUB with per cpu queues that work similar to SLABs queues. With that approach SLUB wins in hackbench:

#!/bin/bash
uname -a
echo "./hackbench 100 process 200000"
./hackbench 100 process 200000
echo "./hackbench 100 process 20000"
./hackbench 100 process 20000
echo "./hackbench 100 process 20000"
./hackbench 100 process 20000
echo "./hackbench 100 process 20000"
./hackbench 100 process 20000
echo "./hackbench 10 process 20000"
./hackbench 10 process 20000
echo "./hackbench 10 process 20000"
./hackbench 10 process 20000
echo "./hackbench 10 process 20000"
./hackbench 10 process 20000
echo "./hackbench 1 process 20000"
./hackbench 1 process 20000
echo "./hackbench 1 process 20000"
./hackbench 1 process 20000
echo "./hackbench 1 process 20000"
./hackbench 1 process 20000

Procs NR SLAB SLUB SLUB+Queuing
----------------------------------------------------
100 200000 2741.3 2764.7 2231.9
100 20000 279.3 270.3 219.0
100 20000 278.0 273.1 219.2
100 20000 279.0 271.7 218.8
10 20000 34.0 35.6 28.8
10 20000 30.3 35.2 28.4
10 20000 32.9 34.6 28.4
1 20000 6.4 6.7 6.5
1 20000 6.3 6.8 6.5
1 20000 6.4 6.9 6.4

SLUB+Q is a merging of SLUB with some queuing concepts from SLAB and a new way of managing objects in the slabs using bitmaps. It uses a percpu queue so that free operations can be properly buffered and a bitmap for managing the free/allocated state in the slabs. It is slightly more inefficient than SLUB (due to the need to place large bitmaps --sized a few words--in some slab pages if there are more than BITS_PER_LONG objects in a slab) but in general does not increase space use too much.

The SLAB scheme of not touching the object during management is adopted. SLUB+Q can efficiently free and allocate cache cold objects without causing cache misses.

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