8292329: Enable CDS shared heap for zero builds

Reviewed-by: shade, erikj, ihse

Author: iklam

make/Images.gmk

@@ -114,6 +114,12 @@ $(eval $(call SetupExecute, jlink_jre, \
 
 JLINK_JRE_TARGETS := $(jlink_jre)
 
+# Optimize CDS shared heap for small heap sizes, which are typically used
+# for small cloud-based apps that have the most critical start-up requirement.
+# The trade-off is that when larger heap sizes are used, the shared heap
+# may need to be relocated at runtime.
+CDS_DUMP_FLAGS = -Xmx128M -Xms128M
+
 # Helper function for creating the CDS archives for the JDK and JRE
 #
 # Param1 - VM variant (e.g., server, client, zero, ...)
@@ -122,6 +128,9 @@ define CreateCDSArchive
   $1_$2_DUMP_EXTRA_ARG := $(if $(filter _nocoops, $2),-XX:-UseCompressedOops,)
   $1_$2_DUMP_TYPE      := $(if $(filter _nocoops, $2),-NOCOOPS,)
 
+  # Only G1 supports dumping the shared heap, so explicitly use G1 if the JVM supports it.
+  $1_$2_CDS_DUMP_FLAGS := $(CDS_DUMP_FLAGS) $(if $(filter g1gc, $(JVM_FEATURES_$1)),-XX:+UseG1GC)
+
   ifeq ($(OPENJDK_TARGET_OS), windows)
     $1_$2_CDS_ARCHIVE := bin/$1/classes$2.jsa
   else
@@ -130,24 +139,26 @@ define CreateCDSArchive
 
   $$(eval $$(call SetupExecute, $1_$2_gen_cds_archive_jdk, \
       WARN := Creating CDS$$($1_$2_DUMP_TYPE) archive for jdk image for $1, \
+      INFO := Using CDS flags for $1: $$($1_$2_CDS_DUMP_FLAGS), \
       DEPS := $$(jlink_jdk), \
       OUTPUT_FILE := $$(JDK_IMAGE_DIR)/$$($1_$2_CDS_ARCHIVE), \
       SUPPORT_DIR := $$(SUPPORT_OUTPUTDIR)/images/jdk, \
       COMMAND := $$(FIXPATH) $$(JDK_IMAGE_DIR)/bin/java -Xshare:dump \
           -XX:SharedArchiveFile=$$(JDK_IMAGE_DIR)/$$($1_$2_CDS_ARCHIVE) \
-          -$1 $$($1_$2_DUMP_EXTRA_ARG) -Xmx128M -Xms128M $$(LOG_INFO), \
+          -$1 $$($1_$2_DUMP_EXTRA_ARG) $$($1_$2_CDS_DUMP_FLAGS) $$(LOG_INFO), \
   ))
 
   JDK_TARGETS += $$($1_$2_gen_cds_archive_jdk)
 
   $$(eval $$(call SetupExecute, $1_$2_gen_cds_archive_jre, \
       WARN := Creating CDS$$($1_$2_DUMP_TYPE) archive for jre image for $1, \
+      INFO := Using CDS flags for $1: $$($1_$2_CDS_DUMP_FLAGS), \
       DEPS := $$(jlink_jre), \
       OUTPUT_FILE := $$(JRE_IMAGE_DIR)/$$($1_$2_CDS_ARCHIVE), \
       SUPPORT_DIR := $$(SUPPORT_OUTPUTDIR)/images/jre, \
       COMMAND := $$(FIXPATH) $$(JRE_IMAGE_DIR)/bin/java -Xshare:dump \
           -XX:SharedArchiveFile=$$(JRE_IMAGE_DIR)/$$($1_$2_CDS_ARCHIVE) \
-          -$1 $$($1_$2_DUMP_EXTRA_ARG) -Xmx128M -Xms128M $$(LOG_INFO), \
+          -$1 $$($1_$2_DUMP_EXTRA_ARG) $$($1_$2_CDS_DUMP_FLAGS) $$(LOG_INFO), \
   ))
 
   JRE_TARGETS += $$($1_$2_gen_cds_archive_jre)