Hotspot should support multiple large page sizes on Windows #23
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…SFT OpenJDK on Windows
nitinsingh130519
changed the title
nitinsingh130519
changed the title
nitinsingh130519
changed the title
swesonga
reviewed
Aug 20, 2024
dhanalla
reviewed
Aug 28, 2024
| @@ -3307,14 +3307,15 @@ static char* allocate_pages_individually(size_t bytes, char* addr, DWORD flags, | |||
| return p_buf; | |||
| } | |||
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| static size_t large_page_init_decide_size() { | |||
| size_t os::win32::large_page_init_decide_size() { | |||
| // print a warning if any large page related flag is specified on command line | |||
| bool warn_on_failure = !FLAG_IS_DEFAULT(UseLargePages) || | |||
| !FLAG_IS_DEFAULT(LargePageSizeInBytes); | |||
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| #define WARN(msg) if (warn_on_failure) { warning(msg); } | |||
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make the macro to allow variable parameters
#define WARN(...) if (warn_on_failure) { warning(VA_ARGS); }
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i made this change in upstream PR openjdk#20758
also validated the gtest
dhanalla
reviewed
Aug 28, 2024
| size = LargePageSizeInBytes; | ||
| } else { | ||
| char buffer[256]; | ||
| snprintf(buffer, sizeof(buffer), "The specified large page size (%d) is not a multiple of the minimum large page size (%d), defaulting to minimum page size.", LargePageSizeInBytes, size); |
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use macro WARN after making it to accept variable parameters.
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This pull request introduces enhancements to the handling of large page sizes in the OpenJDK for Windows systems, aiming to align its capabilities with those observed on Linux platforms. Investigation through SPECJBB benchmarks across various platforms revealed a 16-year-old limitation in handling large pages over 4MB for IA32/AMD64 architectures, with no such constraints for Windows on ARM64.
JBS issue https://bugs.openjdk.org/browse/JDK-8338136
The goal of this change is to overcome the 4MB large page size limitation, thereby enhancing Windows' large page support to match Linux's more flexible handling capabilities. This decision to remove 4MB constraint was influenced by insights from Linux's implementation strategies. The implementation supports multiple large page sizes , specifically excluding the IA32 architecture.
Key changes and bug fixes include enabling Windows support for multiple huge page sizes with -XX:LargePageSizeInBytes, and utilizing logic from JDK-8271195 to use the largest available large page size smaller than LargePageSizeInBytes when available.
This update removes the 4MB limit on AMD64 for Windows, populating the shared array to enable fallback options on all architectures except IA32. The implementation introduces an experimental flag, defaulting to FALSE, to facilitate testing and gradual adoption of these changes. The flag allows users to opt-in to the new large page handling logic, with a warning mechanism implemented for cases where the requested large page size is not a multiple of the OS minimum page size.