RFR: 8293019: [JVMCI] change ratio of libgraal to C1 threads and use one isolate per libgraal thread

[Igor Veresov]

On Wed, 31 Aug 2022 07:27:57 GMT, Doug Simon <dnsimon at openjdk.org> wrote:

> [JDK-8242440](https://bugs.openjdk.org/browse/JDK-8242440) allows the VM to use one isolate per libgraal thread (OIPLT). This has a number of benefits such better isolation of compiler crashes and avoids GC interference between isolates. Experimentation has shown that reducing the ratio of libgraal threads to C1 threads also helps keep the max RSS down. This PR makes OIPLT the default and adds a `JVMCINativeLibraryThreadFraction` flag for configuring the libgraal to C1 thread ratio. The default value for `JVMCINativeLibraryThreadFraction` is `0.33` which means there are 2 C1 threads per libgraal thread.

LGTM

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

Marked as reviewed by iveresov (Reviewer).

PR: https://git.openjdk.org/jdk/pull/10094