[release/7.0] Enable caching of writeable W^X mappings #74589
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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.
ghost
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@jeffschwMSFT do you approve of this backport? |
mangod9
approved these changes
Aug 25, 2022
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@JulieLeeMSFT can we get an approval on Jeff's behalf? Edit: Ah, it was on @tommcdon side. Thanks. |
tommcdon
approved these changes
Aug 25, 2022
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CI failure is #73299 |
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Backport of #74526 to release/7.0
/cc @janvorli
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.
Customer Impact
Performance of workloads with a lot of regular expressions usage can
regress upto 25% without this change compared to .NET 6.
Testing
CI tests, local coreclr / libraries testing, local dotnet/performance benchmarks.
Risk
Low, it just extends lifetime of a RW mapping for executable code writing / modifications until the next mapping is requested.
IMPORTANT: Is this backport for a servicing release? If so and this change touches code that ships in a NuGet package, please make certain that you have added any necessary package authoring and gotten it explicitly reviewed.