[mono][sgen] Fix incorrect condition when checking if we should do a major collection #120432
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…major collection When we are in this method, major sweep hasn't yet finished so we check with some imprecise conservative values. min_heap_size is a conservative lower limit of the actual heap size. Allowance represents how much more we allow the heap to grow after the previous major collection. We were comparing the min_heap_size with the allowance by mistake, when we should have compared it with the next major trigger size (which is the heap_size after the last collection plus the allowance).
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Pull Request Overview
This PR fixes an incorrect condition in the Mono SGEN garbage collector that was causing excessive major garbage collections. The bug was introduced in a previous change and resulted in performance regression from .NET 8 to .NET 9.
Key changes:
- Corrects the major collection trigger logic by comparing minimum heap size against the proper threshold
- Fixes a condition that was incorrectly comparing heap size with allowance instead of total trigger size
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Tagging subscribers to this area: @BrzVlad |
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/ba-g wasm unrelated |
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/backport to release/10.0 |
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Started backporting to release/10.0: https://github.com/dotnet/runtime/actions/runs/18348341019 |
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/backport to release/9.0-staging |
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Started backporting to release/9.0-staging: https://github.com/dotnet/runtime/actions/runs/18348346199 |
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When we are in this method, major sweep hasn't yet finished so we check with some imprecise conservative values. min_heap_size is a conservative lower limit of the actual heap size. Allowance represents how much more we allow the heap to grow after the previous major collection. We were comparing the min_heap_size with the allowance by mistake, when we should have compared it with the next major trigger size (which is the heap_size after the last collection plus the allowance).
Wrong condition added in #98154, causing excessive GCs in some scenarios and regression from .net8 to .net9.
Fixes #119580