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 <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Tino Reichardt <[email protected]>
Closes openzfs#16641

.github/workflows/scripts/qemu-1-setup.sh

@@ -18,19 +18,21 @@ ssh-keygen -t ed25519 -f ~/.ssh/id_ed25519 -q -N ""
 
 # we expect RAM shortage
 cat << EOF | sudo tee /etc/ksmtuned.conf > /dev/null
+# /etc/ksmtuned.conf - Configuration file for ksmtuned
 # https://docs.redhat.com/en/documentation/red_hat_enterprise_linux/7/html/virtualization_tuning_and_optimization_guide/chap-ksm
 KSM_MONITOR_INTERVAL=60
 
 # Millisecond sleep between ksm scans for 16Gb server.
 # Smaller servers sleep more, bigger sleep less.
-KSM_SLEEP_MSEC=10
-KSM_NPAGES_BOOST=300
-KSM_NPAGES_DECAY=-50
-KSM_NPAGES_MIN=64
-KSM_NPAGES_MAX=2048
-
-KSM_THRES_COEF=25
-KSM_THRES_CONST=2048
+KSM_SLEEP_MSEC=30
+
+KSM_NPAGES_BOOST=0
+KSM_NPAGES_DECAY=0
+KSM_NPAGES_MIN=1000
+KSM_NPAGES_MAX=25000
+
+KSM_THRES_COEF=80
+KSM_THRES_CONST=8192
 
 LOGFILE=/var/log/ksmtuned.log
 DEBUG=1

.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