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[release/9.0-staging] Revert "Remove custom allocator." #118279

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@github-actions github-actions bot commented Aug 1, 2025

Backport of #117949 to release/9.0-staging

/cc @ericstj

Customer Impact

  • Customer reported
  • Found internally

The performance of compression on .NET 9.0 was degraded in large production applications running on Windows with many concurrent operations. We tracked down the cause of the regression as due to heap fragmentation and increased CPU time spent when trying to allocate memory in zlib-ng.

Regression

  • Yes
  • No

Regression introduced in .NET 9.0 RC2 -- c62bc5b #105771

Testing

Benchmark created, verified fixed with the change. Customer validated fix as well.
Benchmarks will be added to performance repo if they can be made reliable. This issue issue is difficult to test as it relies on stress scenarios.

Risk

Low. We've done a lot of validation of this. We've shipped with this functionality present in the past.

@ericstj ericstj added Servicing-consider Issue for next servicing release review area-System.IO.Compression labels Aug 1, 2025
@ericstj ericstj self-assigned this Aug 1, 2025
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Tagging subscribers to this area: @dotnet/area-system-io-compression
See info in area-owners.md if you want to be subscribed.

@leecow leecow added Servicing-approved Approved for servicing release and removed Servicing-consider Issue for next servicing release review labels Aug 5, 2025
@leecow leecow modified the milestones: 9.0.10, 9.0.9 Aug 5, 2025
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