RFR: 8358748: Large page size initialization fails with assert "page_size must be a power of 2"

[Amit Kumar]

On Thu, 26 Jun 2025 07:48:43 GMT, Yagmur Eren <duke at openjdk.org> wrote:

> The VM now exits gracefully if `-XX:LargePageSizeInBytes` is set to a non power of two value, instead of asserting. After this change, `SizeTTest.java` failed because the tested values are not valid for `-XX:LargePageSizeInBytes` (`LargePageSizeInBytesConstraintFunc` returns `JVMFlag::VIOLATES_CONSTRAINT`). Therefore, I updated the test to use `NUMASpaceResizeRate`, since I believe that it only requires a flag of type `size_t`.
> 
> Before the change:
> 
> java -XX:+UseLargePages -XX:LargePageSizeInBytes=6 -version
> 
> # A fatal error has been detected by the Java Runtime Environment:
> #
> # Internal Error (workspace/open/src/hotspot/share/runtime/os.cpp:2449), pid=1885945, tid=1885946
> # assert(is_power_of_2(page_size)) failed: page_size must be a power of 2: 0x6
> 
> 
> 
> After the change:
> 
> java -XX:+UseLargePages -XX:LargePageSizeInBytes=6 -version
> 
> LargePageSizeInBytes ( 6 ) must be a power of 2
> Improperly specified VM option 'LargePageSizeInBytes=6'
> Error: Could not create the Java Virtual Machine.
> Error: A fatal exception has occurred. Program will exit.

src/hotspot/share/runtime/flags/jvmFlagConstraintsRuntime.cpp line 141:

> 139:     return JVMFlag::SUCCESS;
> 140:   }
> 141: }

I don't think you need `else` part here.

Suggestion:

  } 
    
  return JVMFlag::SUCCESS;
}

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/25994#discussion_r2174361693