Remove large-memory CopyTo and parser overflow tests#131280
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tannergooding merged 2 commits intoJul 24, 2026
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The three disabled/expensive large-memory tests committed 8GB (CopyTo) or refilled 2GB five times (parser), thrashing swap on 14GB CI agents. Halve the CopyTo footprint to a single overlapping ~4GB buffer, verify only the boundaries (the tail still catches a truncated length), drop the redundant 4GB+256B case, and fill the parser buffer once while restoring only the bytes each case touches. Switch AllocationHelper from Marshal.AllocHGlobal to NativeMemory, and re-enable the two CopyTo tests by removing the dotnet#24139 ActiveIssue. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
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Pull request overview
This PR adjusts several System.Memory.Tests [OuterLoop] scenarios to reduce peak memory and per-test execution cost while keeping coverage of large-buffer behaviors (notably >4GB CopyTo and ~2GB parser overflow).
Changes:
- Updates the large-buffer
Span<T>.CopyTo/ReadOnlySpan<T>.CopyTotests to use a single overlapping >4GB native allocation instead of two separate >4GB allocations. - Refactors the 2GiB parser overflow test to fill the 2GB buffer once and restore only the bytes touched per test case.
- Switches test native allocation helpers from
Marshal.AllocHGlobal/FreeHGlobaltoNativeMemory.Alloc/Free.
Show a summary per file
| File | Description |
|---|---|
| src/libraries/System.Memory/tests/Span/CopyTo.cs | Reworks >4GB Span.CopyTo test to use one overlapping native buffer and fewer assertions. |
| src/libraries/System.Memory/tests/ReadOnlySpan/CopyTo.cs | Mirrors the Span change for ReadOnlySpan.CopyTo with the same allocation strategy. |
| src/libraries/System.Memory/tests/ParsersAndFormatters/Parser/ParserTests.2gbOverflow.cs | Avoids repeated full-buffer refills by reusing a single 2GB span and restoring only mutated bytes. |
| src/libraries/System.Memory/tests/AllocationHelper.cs | Changes native allocation/free implementation to NativeMemory and keeps a global mutex for large allocations. |
Copilot's findings
- Files reviewed: 4/4 changed files
- Comments generated: 3
- AllocationHelper: release the mutex on any failed allocation via finally, not just OutOfMemoryException, so a failure can't leave it held and hang later tests. - CopyTo tests: initialize only the boundary elements instead of filling the whole >4GB buffer, dropping an extra full memory pass while keeping truncation detection. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
tannergooding
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@vcsjones any other feedback on this one? |
vcsjones
approved these changes
Jul 24, 2026
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Fixes #24139.
Removes the three large-memory
[OuterLoop]tests inSystem.Memory.Tests— the twoCopyToLargeSizeTest(Span+ReadOnlySpan) andTestParser2GiBOverflow— rather than trying to keep them alive.These allocated 4–16GB of memory (or repeatedly filled a 2GB buffer) and were flaky on the 14GB outerloop machines, which is what #24139 reports. After looking at what they actually cover, they aren't worth that cost:
>2GB/>4GBcode path.Span<T>.CopyTojust funnels into the nativeMemmove, and the parser case only validates that a full 2GB buffer is consumed and succeeds/fails as expected.Span<T>is itself length-limited, so there is no overflow edge case here that isn't already covered — and better bounded — by the existing bounds/overflow tests.AllocationHelperis left as-is; it is still used by the remaining large-allocation tests (Overflow,Clear,BinarySearch,Base64).Note
This PR description and the code changes were drafted with GitHub Copilot.