Release Note: New jdk.ObjectAllocationSample Event Enabled by Default

A new JFR event, `jdk.ObjectAllocationSample`, is introduced to allow always-on, low-overhead allocation profiling. The event is enabled in both the `default` and `profile` configurations, with a maximum rate of 150 and 300 events/s, respectively. Events `jdk.ObjectAllocationInNewTLAB` and `jdk.ObjectAllocationOutsideTLAB` also detail memory allocations, but have comparatively higher overhead. They were previously disabled in the `default` configuration but are now also disabled in the `profile` configuration to reduce the overhead further.

The impact of this change can be seen in JDK Mission Control (JMC) 8.0, or earlier releases, where the 'TLAB Allocations' page will be missing data. The recommendation is to upgrade to a later version of JMC when the `jdk.ObjectAllocationSample` support is available. Meanwhile, it is possible to enable the `jdk.ObjectAllocationInNewTLAB` and `jdk.ObjectAllocationOutsideTLAB` events in the JMC recording wizard, or edit the .jfc file manually.