Enable caching of writeable W^X mappings #74526
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This change enables caching of the last used writeable mapping for W^X. It was originally disabled by an ifdef, but after we've turned W^X on by default, performance tests have shown a regression in some regex tests. I have investigated those and found that they do excessive amount of jitting (around 50000 methods). Enabling the caching of the last used writeable mapping fixes the regression completely. The caching implementation was present in the sources ever since I've implemented the W^X stuff, but if was disabled by an ifdef. So this change just defines the related symbol and enables the code. The caching basically just keeps a writeable mapping after unmapping until the next mapping request arrives, so it gives an opportunity to reuse it in case of series of mappings of sequential range of executable memory, which happens e.g. in the case mentioned.
mangod9
approved these changes
Aug 24, 2022
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/backport to release/7.0 |
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Started backporting to release/7.0: https://github.com/dotnet/runtime/actions/runs/2927802151 |
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Seeing big improvements in many of the regressed tests from the enabling of W^X: dotnet/perf-autofiling-issues#8171 |
ghost
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This change enables caching of the last used writeable mapping for
W^X. It was originally disabled by an ifdef, but after we've turned W^X
on by default, performance tests have shown a regression in some regex
tests. I have investigated those and found that they do excessive amount
of jitting (around 50000 methods). Enabling the caching of the last used
writeable mapping fixes the regression completely.
The caching implementation was present in the sources ever since I've
implemented the W^X stuff, but if was disabled by an ifdef. So this
change just defines the related symbol and enables the code.
The caching basically just keeps a writeable mapping after unmapping
until the next mapping request arrives, so it gives an opportunity to
reuse it in case of series of mappings of sequential range of executable
memory, which happens e.g. in the case mentioned.