ZTS: Optimize Kernel Same-page Merging (KSM)

Kernel same-page Merging (KSM) allows KVM guests to share identical
memory pages. These shared pages are usually common libraries or other
identical, high-use data.

The current configuration was a bit to lazy - so KSM didn't work very
well. With the new configuration I could run 3 Linux VMs in parralel.

FreeBSD can't benefit from it. But FreeBSD is not so memory hungry in
general, so there is no need for it ;)

Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tino Reichardt <milky-zfs@mcmilk.de>
Closes #16641

.github/workflows/scripts/qemu-5-setup.sh

@@ -14,17 +14,19 @@ PID=$(pidof /usr/bin/qemu-system-x86_64)
 tail --pid=$PID -f /dev/null
 sudo virsh undefine openzfs
 
+# default values per test vm:
+VMs=2
+CPU=2
+
 # definitions of per operating system
 case "$OS" in
+  # FreeBSD can't be optimized via ksmtuned
   freebsd*)
-    VMs=2
-    CPU=3
     RAM=6
     ;;
   *)
-    VMs=2
-    CPU=3
-    RAM=7
+    # Linux can be optimized via ksmtuned
+    RAM=8
     ;;
 esac