RFR: 8370050: Shenandoah: Obsolete ShenandoahPacing option

[David Holmes]

On Thu, 16 Oct 2025 23:46:23 GMT, William Kemper <wkemper at openjdk.org> wrote:

> ShenandoahPacing was removed in this release (26). Rather than have the JVM refuse to start if this option is given, it should give a warning that the option is removed and is ignored and will reject the option in JDK27.
> 
> Testing:
> 
> [0] % ./build/linux-x86_64-server-release/jdk/bin/java -XX:+UseShenandoahGC -XX:+UnlockExperimentalVMOptions -XX:+ShenandoahPacing --version
> OpenJDK 64-Bit Server VM warning: Ignoring option ShenandoahPacing; support was removed in 26.0

src/hotspot/share/runtime/arguments.cpp line 551:

> 549:   { "ZMarkStackSpaceLimit",         JDK_Version::undefined(), JDK_Version::jdk(25), JDK_Version::undefined() },
> 550:   { "G1UpdateBufferSize",           JDK_Version::undefined(), JDK_Version::jdk(26), JDK_Version::jdk(27) },
> 551:   { "ShenandoahPacing",             JDK_Version::jdk(25), JDK_Version::jdk(26), JDK_Version::jdk(27) },

Nit: you didn't actually deprecate the option in 25 so this should have been left as `undefined()`.

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PR Review Comment: https://git.openjdk.org/jdk/pull/27859#discussion_r2438349801