Use peak memory usage as a better proxy for ctest parallelism

[bdice]

Description

Data from #18599 (comment) shows that we need to mark a few tests as requiring more of the GPU to avoid OOM errors. Conversely, we are marking several tests as requiring more than the default (15% of the GPU) which should be safe to run in parallel (and probably failed due to other large-memory tests).

Currently we run our tests in CI with -j20, but we default all tests to requiring 15% of the GPU (so a maximum of 6 tests are able to run in parallel). Our lowest VRAM GPU in CI is an L4 with 24 GB. We should be able to safely run any tests that require <1 GB of memory in parallel (requiring 20 GB at most). We have 7 tests using more than that (shown below).

This PR proposes to run JOIN_TEST, PARQUET_TEST, LARGE_STRINGS_TEST, ORC_TEST, COPYING_TEST, BINARYOP_TEST, and RESHAPE_TEST in isolation (100% of the GPU), while allowing all other tests to be run 14-way parallel (all other tests require 7% of the GPU). This should still allow tests to pass on a 16 GB GPU, if the 14 parallel tests each consume less than 1 GB of GPU memory. Going forward, any new tests that consume more than 1 GB of memory should be set to run with 100% of the GPU, to keep bookkeeping simpler.

Memory usage by test

JOIN_TEST,18.66 GB
PARQUET_TEST,14.34 GB
LARGE_STRINGS_TEST,13.08 GB
ORC_TEST,6.24 GB
COPYING_TEST,6.00 GB
BINARYOP_TEST,5.03 GB
RESHAPE_TEST,3.60 GB
CUDFTABLE_TEST,0.81 GB
MULTIBYTE_SPLIT_TEST,0.81 GB
COMPRESSION_TEST,0.74 GB
HYBRID_SCAN_TEST,0.65 GB
STREAM_IO_MULTIBYTE_SPLIT_TEST,0.56 GB
DATA_CHUNK_SOURCE_TEST,0.47 GB
JSON_TEST,0.35 GB
CSV_TEST,0.23 GB
QUANTILES_TEST,0.08 GB
GROUPBY_TEST,0.07 GB
REPLACE_TEST,0.03 GB
REDUCTIONS_TEST,0.02 GB
ITERATOR_TEST,0.02 GB
TEXT_TEST,0.01 GB
NESTED_JSON_TEST,0.01 GB
STREAM_COMPACTION_TEST,0.01 GB
UTILITIES_TEST,0.01 GB
PARQUET_DELETION_VECTORS_TEST,0.01 GB
STREAM_TEXT_TEST,0.01 GB
STRINGS_TEST,0.00 GB
STREAM_STRINGS_TEST,0.00 GB
INTEROP_TEST,0.00 GB
ROLLING_TEST,0.00 GB
FST_TEST,0.00 GB
LOGICAL_STACK_TEST,0.00 GB
TRANSPOSE_TEST,0.00 GB
MERGE_TEST,0.00 GB
STREAM_MERGE_TEST,0.00 GB
PARTITIONING_TEST,0.00 GB
SORT_TEST,0.00 GB
REPLACE_NULLS_TEST,0.00 GB
STREAM_COPYING_TEST,0.00 GB
CLAMP_TEST,0.00 GB
UNARY_TEST,0.00 GB
TRANSFORM_TEST,0.00 GB
DEVICE_ATOMICS_TEST,0.00 GB
ROUND_TEST,0.00 GB
AST_TEST,0.00 GB
TIMEZONE_TEST,0.00 GB
FILLING_TEST,0.00 GB
STREAM_IO_ORC_TEST,0.00 GB
BITMASK_TEST,0.00 GB
LABEL_BINS_TEST,0.00 GB
JSON_WRITER_TEST,0.00 GB
FACTORIES_TEST,0.00 GB
STREAM_IO_HYBRID_SCAN_TEST,0.00 GB
STREAM_IO_PARQUET_TEST,0.00 GB
COLUMN_TEST,0.00 GB
SEARCH_TEST,0.00 GB
FIXED_POINT_TEST,0.00 GB
LISTS_TEST,0.00 GB
STRUCTS_TEST,0.00 GB
HASHING_TEST,0.00 GB
STREAM_TRANSPOSE_TEST,0.00 GB
STREAM_SORTING_TEST,0.00 GB
STREAM_IO_CSV_TEST,0.00 GB
JSON_WHITESPACE_NORMALIZATION_TEST,0.00 GB
JSON_PATH_TEST,0.00 GB
JSON_QUOTE_NORMALIZATION_TEST,0.00 GB
STREAM_IO_JSON_TEST,0.00 GB
STREAM_TRANSFORM_TEST,0.00 GB
STREAM_JOIN_TEST,0.00 GB
IS_SORTED_TEST,0.00 GB
DICTIONARY_TEST,0.00 GB
SCALAR_TEST,0.00 GB
FILTER_TEST,0.00 GB
DATETIME_OPS_TEST,0.00 GB
STREAM_STREAM_COMPACTION_TEST,0.00 GB
TIMESTAMPS_TEST,0.00 GB
ENCODE_TEST,0.00 GB
REPLACE_NANS_TEST,0.00 GB
STREAM_DICTIONARY_TEST,0.00 GB
STREAM_PARTITIONING_TEST,0.00 GB
STREAM_GROUPBY_TEST,0.00 GB
ROW_IR_TEST,0.00 GB
STREAM_LISTS_TEST,0.00 GB
STREAM_QUANTILE_TEST,0.00 GB
TABLE_TEST,0.00 GB
STREAM_ROLLING_TEST,0.00 GB
STREAM_REPLACE_TEST,0.00 GB
STREAM_RESHAPE_TEST,0.00 GB
STREAM_REDUCTION_TEST,0.00 GB
STREAM_FILLING_TEST,0.00 GB
SPAN_TEST,0.00 GB
NORMALIZE_REPLACE_TEST,0.00 GB
STREAM_HASHING_TEST,0.00 GB
STREAM_LABELING_BINS_TEST,0.00 GB
STREAM_CONCATENATE_TEST,0.00 GB
STREAM_NULL_MASK_TEST,0.00 GB
STREAM_SEARCH_TEST,0.00 GB
STREAM_TABLE_EQUALITY_TEST,0.00 GB
TYPE_INFERENCE_TEST,0.00 GB
STREAM_ROARING_BITMAP_TEST,0.00 GB
STREAM_BINARYOP_TEST,0.00 GB
STREAM_ROUND_TEST,0.00 GB
STREAM_DATETIME_TEST,0.00 GB
STREAM_UNARY_TEST,0.00 GB
STREAM_SCALAR_TEST,0.00 GB
DISPATCHER_TEST,0.00 GB
JIT_PARSER_TEST,0.00 GB
ROW_SELECTION_TEST,0.00 GB
STREAM_POOL_TEST,0.00 GB
TRAITS_TEST,0.00 GB
FILEPATH_SOURCE_TEST,N/A
JSON_TREE_CSR_TEST,N/A
ROARING_BITMAP_TEST,N/A
ROW_OPERATOR_TEST,N/A
STREAM_COLUMN_VIEW_TEST,N/A
STREAM_IDENTIFICATION_TEST,N/A
TRANSFORM_LTO_TEST,N/A
VARIANT_EXTRACT_TEST,N/A

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[davidwendt]

Could you include LARGE_STRINGS_TEST in the 100% GPU case as well?
It is handling the memory resource independently and so did not show up in the statistics in #18599
But by definition, I would expect this to require a large amount of device memory.
I will look at fixing this in 18599.

[davidwendt]

You may want to be careful to not overfit to the current CI infrastructure. And also allow room for future tests to grow a bit.
Unless you are trying to encourage keeping memory constraints low in tests in which case you have my full support.

[bdice]

You may want to be careful to not overfit to the current CI infrastructure. And also allow room for future tests to grow a bit. Unless you are trying to encourage keeping memory constraints low in tests in which case you have my full support.

Agreed -- I am mostly experimenting right now. I am trying to fit into what I think would work on a 16 GB GPU, although our smallest GPU in CI is 24 GB. I am suspecting our peak memory usage for each test may not be accurate, since running 10 tests in parallel instead of 6 tests fails even on a 24 GB GPU. Perhaps there is overhead in loading libcudf from each process? I'm not sure.

Also, I'm a little sad, because the runtimes for the test suite seem to have gone up a bit with this PR compared to another PR I looked at. Previously we allowed some tests to run in parallel with the larger tests (we had some that requested 30% or 70% of the GPU). Perhaps we should accept that increase in runtime in exchange for greater stability? Or perhaps we should mark the larger tests as requiring 70% instead of 100% of the GPU, therefore allowing two other "small" tests to run at the same time? I'm not sure.

[davidwendt]

Also, I'm a little sad, because the runtimes for the test suite seem to have gone up a bit with this PR compared to another PR I looked at. Previously we allowed some tests to run in parallel with the larger tests (we had some that requested 30% or 70% of the GPU). Perhaps we should accept that increase in runtime in exchange for greater stability?

I also took a quick look at runtime and I would totally accept an increase in runtime to make this easier to maintain.
So I rather something simple that can be easily adjusted over time so we don't have to rework this too often.

[bdice]

Oooh, I wonder if there's something going on here with "pool" being the default memory resource. We should probably use "async" so the processes can share a driver-managed pool. Running multiple tests in parallel is probably allocating many large pools, each of which takes half of what's left of free memory until the last test gets 1/64 of the GPU memory or something like that. (I don't think the tests are sharing a single pool resource.)

[davidwendt]

Oooh, I wonder if there's something going on here with "pool" being the default memory resource. We should probably use "async" so the processes can share a driver-managed pool. Running multiple tests in parallel is probably allocating many large pools, each of which takes half of what's left of free memory until the last test gets 1/64 of the GPU memory or something like that. (I don't think the tests are sharing a single pool resource.)

Ok. The default rmm-mode can be controlled with GTEST_CUDF_RMM_MODE environment variable. Perhaps this should be set in the CI script? Or do you think we should change the default for everybody?

[bdice]

The default should be async and not pool, imo. We have been migrating lots of workloads to async over pool because the performance is not significantly different and async is much easier to use with multiple applications.

[bdice]

Looks like the failures are now cudf_identify_stream_usage found unexpected stream!. I'll try to take a look at this but it may be late next week. @davidwendt If you're interested in looking sooner, that would be welcome!

[vuule]

Also, I'm a little sad, because the runtimes for the test suite seem to have gone up a bit with this PR compared to another PR I looked at.

Could it be because the pool is not used?

[davidwendt]

I spent some time on this today. It appears the async memory resource is incompatible with the stream-adaptor/checker. The first problem is that when setting up the memory resource in the gtest main, the cuda_async_memory_resource constructor does a do_allocate() and free_allocate() without a stream
https://github.com/rapidsai/rmm/blob/0c9fe21266680973c390721e86454a885b444869/cpp/include/rmm/mr/device/cuda_async_memory_resource.hpp#L145-L149

    // Allocate and immediately deallocate the initial_pool_size to prime the pool with the
    // specified size
    auto const pool_size = initial_pool_size.value_or(free / 2);
    auto* ptr            = do_allocate(pool_size, cuda_stream_default);
    do_deallocate(ptr, pool_size, cuda_stream_default);

These cause the stream-checker to throw an error because the stream-adaptor is loaded via LD_PRELOAD there is no simple way to delay the check and the gtest fails inside of main() before any tests begin.
I tried setting up environment variables and commenting out pieces of the adapter code to let the memory resource be created but the gtests just seem to fail later for some reason -- it was not immediately obvious why and looks like it may require some more significant investigation to make async work with the stream-checker.

This brings into question the value of the stream-checker as well. Perhaps it needs some rework or perhaps we could turn it off by default for ctest and use it only with the cuda or pool resource. There have been recent issues with running it on ARM systems and with PTDS enabled. We should probably debate this in a separate issue.

Another thought is if we could possibly figure out a way to set the pool size for those 15% cases, etc so they allocate less initial memory.

[vyasr]

We can certainly look into reworking the stream testing utility or reassessing how we use it. I'm skeptical that we are really confident enough yet in our stream hygiene to remove its usage entirely, but maybe we could run it on a more limited basis like we run the compute sanitizer tests. Making the stream checker work with more cases (such as with the async pool issue described above) is probably possible but nontrivial.

[vyasr]

@bdice do we still want this PR? IIRC you found that it didn't actually improve CI times?

[bdice]

I needed to revisit it to determine whether the CI time regressions were due to the memory resource change, oversubscription, or something else. I think the changes in this are probably desirable for maintainability, but need a bit of investigation on the CI time regression.

[vyasr]

The stream checker should no longer be the blocker here now that we've switched over to using compute-sanitizer APIs for that purpose. That still may not mean we want this PR though.

[vyasr]

@bdice now that benchmarks are using the async mr as of #23586 it's probably worth at least attempting that change for tests again. It may be worthwhile to separate the async mr change from the peak memory usage change so that both don't have to be bundled into this one PR.

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📝 Walkthrough

Summary by CodeRabbit

• Tests
  • Improved GPU memory scheduling across the test suite to better support varying workloads.
  • Added documentation for GPU memory allocation guidelines.
  • Test memory reporting now highlights only tests exceeding 1 GB, with peak usage shown in gigabytes to two decimal places.
  • Updated allocation settings for more efficient GPU resource use.
• Chores
  • Changed the default memory allocation mode to asynchronous allocation when no override is provided.

Walkthrough

Changes

The PR updates GPU test memory allocation defaults and assignments, changes the fallback RMM mode to async, and reports only tests using more than 1 GB of memory.

Changes

GPU memory configuration

Layer / File(s)	Summary
GPU allocation policy and test assignments cpp/tests/CMakeLists.txt	The default test allocation changes from 15% to 7%. Selected tests use 100% allocation, obsolete overrides are removed, and the allocation rules are documented.
RMM allocation mode default cpp/include/cudf_test/testing_main.hpp	The default RMM mode changes from pool to async when no environment or CLI override is set.
Peak-memory reporting cpp/scripts/gtest_memory_usage.sh	The script stores test results, filters out usage at or below 1 GB, and reports remaining values in GB with two decimal places.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Merge Risk: ⚪ Minimal · up to a5a9e

The change adjusts test parallelism based on measured peak GPU memory usage, with no actionable merge-blocking risk remaining beyond normal checks and review.

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In `@cpp/tests/CMakeLists.txt`:
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