[libcudf] Route dictionary encode temp allocations through `memory_resources` by nirandaperera · Pull Request #23642 · NVIDIA/cudf

nirandaperera · 2026-08-12T22:53:33Z

Description

Depends on #23665

A part of #20780.

Port dictionary encode / decode (public + detail APIs and implementations) to take cudf::memory_resources, routing output and temporary allocations explicitly.
Update dictionary encode/decode tests (and drop stale row-operator TODOs) so they exercise the new resource pair.
Duplicate the narrow fixed-width/string gather plumbing needed so encode/decode can pass memory_resources into detail::gather on this base; list/segmented gather production is left on the existing single-ref APIs via output_mr.

Test plan

DICTIONARY_TEST --gtest_filter='DictionaryEncode*:DictionaryDecode*'
ROW_OPERATOR_TEST --gtest_filter='TypedTableView*:NaNTableView*:RowOperator*'

Checklist

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

copy-pr-bot · 2026-08-12T22:53:37Z

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Port encode/decode APIs and tests to explicit output/temporary resources, and duplicate the narrow fixed-width/string gather plumbing required to pass memory_resources into detail::gather without the list gather slice.

davidwendt · 2026-08-18T21:04:19Z

Just curious. What is the significance of the [cudf] in the PR title?

coderabbitai · 2026-08-18T21:07:15Z

No actionable comments were generated in the recent review. 🎉

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📥 Commits

Reviewing files that changed from the base of the PR and between 9195029 and b295e98.

📒 Files selected for processing (4)

cpp/include/cudf/detail/gather.hpp
cpp/include/cudf/dictionary/detail/encode.hpp
cpp/src/dictionary/decode.cu
cpp/src/dictionary/encode.cu

🚧 Files skipped from review as they are similar to previous changes (4)

cpp/src/dictionary/decode.cu
cpp/include/cudf/dictionary/detail/encode.hpp
cpp/include/cudf/detail/gather.hpp
cpp/src/dictionary/encode.cu

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📝 Walkthrough

Summary by CodeRabbit

New Features
- Gather and dictionary encoding/decoding APIs now support separate memory resources for returned results and temporary processing.
- Improved memory-resource control across string, list, nested, and dictionary operations.
Bug Fixes
- Improved consistency by routing temporary allocations and returned data through their designated resources.
Tests
- Updated dictionary operation tests for explicit stream and memory-resource handling.
- Removed obsolete testing notes.

Walkthrough

Changes

Memory Resource Migration

Layer / File(s)	Summary
Gather resource routing `cpp/include/cudf/copying.hpp`, `cpp/include/cudf/detail/gather.*`, `cpp/src/copying/gather.cu`	Gather APIs now accept `cudf::memory_resources`. Returned columns and masks use the output resource. Temporary buffers and device views use the temporary resource.
Offset and string resource routing `cpp/include/cudf/detail/sizes_to_offsets_iterator.cuh`, `cpp/include/cudf/strings/detail/gather.cuh`, `cpp/include/cudf/strings/detail/strings_children.cuh`	Offset and string gathering separates output allocations from temporary scan and copy allocations.
Dictionary resource migration `cpp/include/cudf/dictionary/*/.hpp`, `cpp/src/dictionary/.cu`, `cpp/include/cudf_test/column_wrapper.hpp`, `cpp/tests/dictionary/`, `cpp/tests/row_operator/row_operator_tests.cu`	Dictionary encode and decode use grouped memory resources. Tests pass fixture streams and resources explicitly, and obsolete allocation TODOs are removed.

Estimated code review effort: 4 (Complex) | ~45 minutes

Merge Risk: 🔵 Low · up to b295e

Dictionary encode/decode now routes allocations through caller-selected memory resources, but the empty-string gather path can still use the default resource. This is a bounded risk for custom memory-resource users and requires explicit owner follow-up.

Possibly related PRs

NVIDIA/cudf#23706: Both changes modify make_offsets_child_column and string-offset allocation paths.

Suggested reviewers: igorpeshansky, vyasr, wence-

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 29.41% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately identifies the primary dictionary allocation change to use memory_resources.
Description check	✅ Passed	The description clearly explains the API, allocation-routing, test, and gather-plumbing changes.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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Actionable comments posted: 2

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Inline comments:
In `@cpp/include/cudf/detail/gather.hpp`:
- Around line 24-25: Update the `@copydoc` signature for cudf::gather in the
gather declaration to reference cudf::memory_resources instead of
rmm::device_async_resource_ref, then run the Doxygen check script to verify the
documentation.

In `@cpp/include/cudf/strings/detail/gather.cuh`:
- Around line 228-232: Update the empty-output branch in the gather
implementation to call make_empty_column with the current stream and output_mr,
ensuring the returned string column uses the caller-selected output memory
resource.

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📥 Commits

Reviewing files that changed from the base of the PR and between 215888d and 6d7b2ea.

📒 Files selected for processing (15)

cpp/include/cudf/copying.hpp
cpp/include/cudf/detail/gather.cuh
cpp/include/cudf/detail/gather.hpp
cpp/include/cudf/detail/sizes_to_offsets_iterator.cuh
cpp/include/cudf/dictionary/detail/encode.hpp
cpp/include/cudf/dictionary/encode.hpp
cpp/include/cudf/strings/detail/gather.cuh
cpp/include/cudf/strings/detail/strings_children.cuh
cpp/include/cudf_test/column_wrapper.hpp
cpp/src/copying/gather.cu
cpp/src/dictionary/decode.cu
cpp/src/dictionary/encode.cu
cpp/tests/dictionary/decode_test.cpp
cpp/tests/dictionary/encode_test.cpp
cpp/tests/row_operator/row_operator_tests.cu

💤 Files with no reviewable changes (1)

cpp/tests/row_operator/row_operator_tests.cu

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vyasr

Thanks, looks solid.

davidwendt · 2026-08-18T21:08:01Z

                               data_type indices_type,
                               cuda::stream_ref stream,
-                               rmm::device_async_resource_ref mr);
+                               cudf::memory_resources mr);


Seems odd that the include statements did not change for this.

@davidwendt I am not sure I understood you. memory_resources come from cudf/utilities/memory_resource.hpp which defines get_current_device_resource_ref() as well.

We changed namespace from rmm to cudf. I would not think both classes are defined in the same header file. It is likely that cudf/utilities/memory_resource.hpp transitively includes an rmm header which is not something we should rely on but this change removes that as well I suppose.

nirandaperera · 2026-08-18T21:29:20Z

Just curious. What is the significance of the [cudf] in the PR title?

I meant to use [libcudf] to mean that only c++ is affected. But I always mess this up 😅

davidwendt · 2026-08-18T21:41:06Z

Just curious. What is the significance of the [cudf] in the PR title?

I meant to use [libcudf] to mean that only c++ is affected. But I always mess this up 😅

We have a label for libcudf. Should we all be doing this?

davidwendt · 2026-08-18T21:59:06Z

Some new APIs were just added/merged in here: #23534

bdice · 2026-08-19T02:51:26Z

Just curious. What is the significance of the [cudf] in the PR title?

I meant to use [libcudf] to mean that only c++ is affected. But I always mess this up 😅

We have a label for libcudf. Should we all be doing this?

@nirandaperera I would just remove the [...] tags from your PR titles. It's not really necessary.

bdice · 2026-08-19T02:53:15Z

                   bool nullify_out_of_bounds,
-                   rmm::cuda_stream_view stream)
+                   rmm::cuda_stream_view stream,
+                   rmm::device_async_resource_ref temp_mr = cudf::get_current_device_resource_ref())


I proposed to @nirandaperera offline that we should make every API accept cudf::memory_resources (even if it only uses a temporary memory resource). That way we have a uniform API at the call site and callers don't have to think about whether the function needs output, temporary, or both.

I am pretty sure I would like to see that here.

nirandaperera added improvement Improvement / enhancement to an existing function non-breaking Non-breaking change labels Aug 12, 2026

github-actions Bot assigned nirandaperera Aug 12, 2026

github-actions Bot added the libcudf Affects libcudf (C++/CUDA) code. label Aug 12, 2026

bdice mentioned this pull request Aug 13, 2026

[cudf] Adding memory_resources support for column wrappers #23581

Merged

3 tasks

nirandaperera force-pushed the dictionary-encode-memory-resources branch from 0c231f1 to 9a1a985 Compare August 14, 2026 18:42

nirandaperera mentioned this pull request Aug 14, 2026

Memory-resource porting checklist for current resource free CUDF_TEST_EXPECT_[COLUMNS/TABLES]_EQUAL use #23668

Open

17 tasks

igorpeshansky mentioned this pull request Aug 15, 2026

[cudf] Thread memory resources through equality/hash row preprocessing #23665

Merged

3 tasks

nirandaperera force-pushed the dictionary-encode-memory-resources branch 2 times, most recently from 5280c4f to b292deb Compare August 17, 2026 20:04

nirandaperera changed the base branch from main to pull-request/23665 August 17, 2026 21:41

nirandaperera changed the base branch from pull-request/23665 to main August 17, 2026 21:43

nirandaperera changed the base branch from main to pull-request/23556 August 17, 2026 22:20

nirandaperera changed the base branch from pull-request/23556 to pull-request/23665 August 17, 2026 22:20

nirandaperera changed the title ~~[cudf] Route dictionary encode and gather temps through memory_resources~~ [cudf] Route dictionary encode temp allocations through memory_resources Aug 17, 2026

nirandaperera changed the base branch from pull-request/23665 to main August 17, 2026 22:44

Wire dictionary encode/decode through memory_resources

6d7b2ea

Port encode/decode APIs and tests to explicit output/temporary resources, and duplicate the narrow fixed-width/string gather plumbing required to pass memory_resources into detail::gather without the list gather slice.

nirandaperera force-pushed the dictionary-encode-memory-resources branch from b292deb to 6d7b2ea Compare August 18, 2026 21:00

nirandaperera marked this pull request as ready for review August 18, 2026 21:00

nirandaperera requested a review from a team as a code owner August 18, 2026 21:00

nirandaperera requested review from davidwendt and igorpeshansky August 18, 2026 21:00

coderabbitai Bot reviewed Aug 18, 2026

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Comment thread cpp/include/cudf/detail/gather.hpp Outdated

Comment thread cpp/include/cudf/strings/detail/gather.cuh

vyasr approved these changes Aug 18, 2026

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davidwendt reviewed Aug 18, 2026

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precommit

9195029

davidwendt mentioned this pull request Aug 18, 2026

Use dictionary indices in join functions #23534

Merged

3 tasks

nirandaperera changed the title ~~[cudf] Route dictionary encode temp allocations through memory_resources~~ [libcudf] Route dictionary encode temp allocations through memory_resources Aug 18, 2026

minor changes

b295e98

This was referenced Aug 18, 2026

Migrate Nanoarrow test helpers to memory_resources #23609

Open

Migrate T-digest test helpers to memory_resources #23608

Open

bdice reviewed Aug 19, 2026

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Description

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