Add context for custom GC tunings (#11651)

Signed-off-by: Andrew Ross <[email protected]>

distribution/src/config/jvm.options

@@ -38,12 +38,12 @@
 8-10:-XX:+UseCMSInitiatingOccupancyOnly
 
 ## G1GC Configuration
-# NOTE: G1 GC is only supported on JDK version 10 or later
-# to use G1GC, uncomment the next two lines and update the version on the
-# following three lines to your version of the JDK
-# 10:-XX:-UseConcMarkSweepGC
-# 10:-XX:-UseCMSInitiatingOccupancyOnly
+# NOTE: G1GC is the default GC for all JDKs 11 and newer
 11-:-XX:+UseG1GC
+# See https://github.com/elastic/elasticsearch/pull/46169 for the history
+# behind these settings, but the tl;dr is that default values can lead
+# to situations where heap usage grows enough to trigger a circuit breaker
+# before GC kicks in.
 11-:-XX:G1ReservePercent=25
 11-:-XX:InitiatingHeapOccupancyPercent=30