We had this exact issue…
XX:MaxPermSize=256M -Xms128M -Xmx1024M -XX:-DisableExplicitGC
You need to change the settings for the memory allocated to your java process. You are only using 1GB of memory. Go to alfrescoinstall/tomcat/bin/setenv.sh and modify this line
JAVA_OPTS="-XX:MaxPermSize=256M -Xms128M -Xmx4096M $JAVA_OPTS " # java-memory-settings
As you can see this one is set to 4GB of memory. Make sure not to set it over what you actually have on the server for memory.