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Overlayfs and Java Application Memory Usage

Hi Folks,
Assume I am using Overlay FS in my docker implementation, does that mean I can save memory (RAM) for JVM in a scenario where I spin 10 tomcat containers from same base image that has identical JDK version (as the JDK comes from same base image).
Each Tomcat I configure with JVM heap space of 4 Gig, my understanding is it will still take 4 Gig * 10=40 Gig of RAM.
Is the only area where overlay FS helps in terms of page cache (and saving RAM) is where my Java code loads native shared library?
Has anybody running this in production? Can you please share your findings on this line?

What the relation between overlayFS (for File System) and RAM?

Page Caching, you can read about it here, https://docs.docker.com/engine/userguide/storagedriver/overlayfs-driver/