Disable copy/move ctors and operator= from free_list classes

[harrism]

Fixes #861.

An implicit copy of free_list was being used instead of a reference, which led to duplicate allocations. This never manifested until after #851 because previously the locally modified copy of a free list was being merged into an MR-owned free list. When we removed one of the places where we merged free lists, this copy resulted in the changes to free lists being lost. This only manifested in PTDS usage, but likely would also manifest in use cases with multiple non-default streams.

[harrism]

I've noticed some impact on the MULTI_STREAM_ALLOCATIONS_BENCH. Sometimes there appears to be some oversynchronization effect on performance. Here I ran it twice in a row, and the first run got the perf I expected, but the 4-stream version ran slower the second time:

(rapids) rapids@compose:~/rmm/build/release$ gbenchmarks/MULTI_STREAM_ALLOCATIONS_BENCH -r pool          
2021-09-01T17:55:24+10:00
Running gbenchmarks/MULTI_STREAM_ALLOCATIONS_BENCH
Run on (16 X 3600 MHz CPU s)
CPU Caches:
  L1 Data 32 KiB (x8)
  L1 Instruction 32 KiB (x8)
  L2 Unified 512 KiB (x8)
  L3 Unified 16384 KiB (x2)
Load Average: 2.26, 2.67, 2.41
***WARNING*** CPU scaling is enabled, the benchmark real time measurements may be noisy and will incur extra overhead.
--------------------------------------------------------------------------------------------------
Benchmark                                        Time             CPU   Iterations UserCounters...
--------------------------------------------------------------------------------------------------
BM_MultiStreamAllocations/pool_mr/1/4/0       2832 us         2831 us          247 items_per_second=1.41287k/s
BM_MultiStreamAllocations/pool_mr/2/4/0       1447 us         1447 us          475 items_per_second=2.76504k/s
BM_MultiStreamAllocations/pool_mr/4/4/0        734 us          734 us          939 items_per_second=5.45189k/s

(rapids) rapids@compose:~/rmm/build/release$ gbenchmarks/MULTI_STREAM_ALLOCATIONS_BENCH -r pool
2021-09-01T17:55:38+10:00
Running gbenchmarks/MULTI_STREAM_ALLOCATIONS_BENCH
Run on (16 X 3600 MHz CPU s)
CPU Caches:
  L1 Data 32 KiB (x8)
  L1 Instruction 32 KiB (x8)
  L2 Unified 512 KiB (x8)
  L3 Unified 16384 KiB (x2)
Load Average: 2.12, 2.62, 2.40
***WARNING*** CPU scaling is enabled, the benchmark real time measurements may be noisy and will incur extra overhead.
--------------------------------------------------------------------------------------------------
Benchmark                                        Time             CPU   Iterations UserCounters...
--------------------------------------------------------------------------------------------------
BM_MultiStreamAllocations/pool_mr/1/4/0       2875 us         2874 us          247 items_per_second=1.39185k/s
BM_MultiStreamAllocations/pool_mr/2/4/0       1489 us         1488 us          444 items_per_second=2.6878k/s
BM_MultiStreamAllocations/pool_mr/4/4/0       2165 us         2164 us          941 items_per_second=1.84812k/s

[codereport]

lgtm 👍

[jlowe]

Excellent find! I verified the C++ and Java unit tests pass with PTDS enabled after this change.

[jrhemstad]

@gpucibot merge