Do not set vm.max_map_count when unnecessary (#31285)

This commit modifies the Sys V init startup scripts to only modify
vm.max_map_count if needed. In this case, needed means that the current
value is less than our default value of 262144 maps.

Author: majormoses

distribution/deb/src/main/packaging/init.d/elasticsearch

@@ -147,7 +147,7 @@ case "$1" in
 		ulimit -l $MAX_LOCKED_MEMORY
 	fi
 
-	if [ -n "$MAX_MAP_COUNT" -a -f /proc/sys/vm/max_map_count ]; then
+	if [ -n "$MAX_MAP_COUNT" -a -f /proc/sys/vm/max_map_count -a "$MAX_MAP_COUNT" -ge $(cat /proc/sys/vm/max_map_count) ]; then
 		sysctl -q -w vm.max_map_count=$MAX_MAP_COUNT
 	fi
 

distribution/rpm/src/main/packaging/init.d/elasticsearch

@@ -114,7 +114,7 @@ start() {
     if [ -n "$MAX_LOCKED_MEMORY" ]; then
         ulimit -l $MAX_LOCKED_MEMORY
     fi
-    if [ -n "$MAX_MAP_COUNT" -a -f /proc/sys/vm/max_map_count ]; then
+    if [ -n "$MAX_MAP_COUNT" -a -f /proc/sys/vm/max_map_count -a "$MAX_MAP_COUNT" -ge $(cat /proc/sys/vm/max_map_count) ]; then
         sysctl -q -w vm.max_map_count=$MAX_MAP_COUNT
     fi
 

qa/vagrant/src/test/resources/packaging/tests/70_sysv_initd.bats

@@ -182,3 +182,32 @@ setup() {
 
     service elasticsearch stop
 }
+
+# Ensures that if $MAX_MAP_COUNT is less than the set value on the OS
+# it will be updated
+@test "[INIT.D] sysctl is run when the value set is too small" {
+  # intentionally a ridiculously low number
+  sysctl -q -w vm.max_map_count=100
+  start_elasticsearch_service
+  max_map_count=$(sysctl -n vm.max_map_count)
+  stop_elasticsearch_service
+
+  [ $max_map_count = 262144 ]
+
+}
+
+# Ensures that if $MAX_MAP_COUNT is greater than the set vaule on the OS
+# we do not attempt to update it this should cover equality as well as I think
+# we can trust that equality operators work as intended.
+@test "[INIT.D] sysctl is not run when it already has a larger or equal value set" {
+  # intentionally set to the default +1
+  sysctl -q -w vm.max_map_count=262145
+  start_elasticsearch_service
+  max_map_count=$(sysctl -n vm.max_map_count)
+  stop_elasticsearch_service
+
+  # default value +1
+  [ $max_map_count = 262145 ]
+
+}
+