automatic memory for kvm balooning guests using virsh

virshautomem.sh

#!/bin/bash

# can be intsalled as a systemd service via
# sudo systemctl edit --full --force virshautomem
#
# [Unit]
# Description=virsh auto memory allocation for ballooning vms
# 
# [Service]
# ExecStart=/usr/local/bin/virshautomem.sh -d
# Restart=always
# RestartSec=15s
#
# [Install]
# WantedBy=default.target

# memory step size in MB to increase/decrease
STEP_MB=512
# minimum memory to assign
MIN_MEMORY=$((2 * 1024 * 1024))
# lower and upper threshold in percent of complete assigned memory
LOWTHRES=12
UPTHRES=17

# Retrieve the connection URI
# uri=$(virsh uri)
uri="qemu:///system"

daemon=0
if [[ "$1" == "-d" ]]; then
    daemon=1;
    echo "running as daemon"
fi

while
    # Retrieve a list of running VMs
    running_vms=$(virsh --connect "$uri" list --name --state-running)

    # echo "checking running vms: $running_vms"
    # Iterate over each VM
    for vm_name in $running_vms; do
      # Retrieve VM XML configuration
        vm_xml=$(virsh --connect "$uri" dumpxml "$vm_name")


        # echo "checking $vm_name"
        # echo "$vm_xml"

        # Check if the VM has ballooning support
        if echo "$vm_xml" | grep -q '<memballoon'; then
            echo -n "adjusting memory for VM: $vm_name: "
            virsh --connect "$uri" dommemstat --domain "$vm_name" --period 5 > /dev/null

            # Extract maximum memory from VM info using xmllint and XPath
            max_memory_value=$(echo "$vm_xml" | xmllint --xpath 'string(/domain/memory)' -)
            max_memory_unit=$(echo "$vm_xml" | xmllint --xpath 'string(/domain/memory/@unit)' -)

            # Convert max_memory_value to kilobytes
            case $max_memory_unit in
                k | kb | KiB)
                    MAX_MEMORY=$max_memory_value
                    ;;
                m | mb | MiB)
                    MAX_MEMORY=$(($max_memory_value * 1024))
                    ;;
                g | gb | GiB)
                    MAX_MEMORY=$(($max_memory_value * 1024 * 1024))
                    ;;
                t | tb)
                    MAX_MEMORY=$(($max_memory_value * 1024 * 1024 * 1024))
                    ;;
                *)
                    echo "Unsupported memory unit: $max_memory_unit"
                    continue
                    ;;
            esac

            # Retrieve memory statistics
            mem_stat=$(virsh --connect "$uri" dommemstat "$vm_name")
            current_memory=$(echo "$mem_stat" | awk '/actual/ { print $2 }')
            available_memory=$(echo "$mem_stat" | awk '/usable/ { print $2 }')

            if [ "$available_memory" = "" ]; then
                echo "unable to detect available memory, ensure balloning driver installed and set up"
                continue
            fi

            # Calculate memory thresholds
            lower_threshold=$(($MAX_MEMORY * $LOWTHRES / 100))
            upper_threshold=$(($MAX_MEMORY * $UPTHRES / 100))

            # Adjust memory allocation
            if ((available_memory < lower_threshold)); then
                echo -n "increase "
                new_memory=$(($current_memory + ($STEP_MB * 1024)))
            elif ((available_memory > upper_threshold)); then
                echo -n "decrease "
                new_memory=$(($current_memory - ($STEP_MB * 1024)))
            else
                echo "keeping current $(($current_memory / 1024 ))M avail: $(($available_memory / 1024))M | lowt: $(($lower_threshold / 1024 ))M | upt: $(($upper_threshold / 1024  ))M"
                continue
            fi

            # echo "NEW $new_memory"

            # Ensure the new memory does not exceed the maximum
            if (($new_memory > $MAX_MEMORY)); then
                new_memory=$MAX_MEMORY
                # echo "assigning MAX $new_memory"
            fi

            # Ensure the new memory does not fall below the minimum
            if (($new_memory < $MIN_MEMORY)); then
                new_memory=$MIN_MEMORY
                # echo "assigning MIN $new_memory"
            fi

            #echo "c $current_memory, a: $available_memory, lt: $lower_threshold, ut: $upper_threshold, new: $new_memory"
            echo "max: $(($MAX_MEMORY / 1024 ))M | cur: $(($current_memory / 1024 ))M | avail: $(($available_memory / 1024 ))M | lowt: $(($lower_threshold / 1024  ))M | upt: $(($upper_threshold / 1024 ))M => $(($new_memory / 1024 ))M"

            # Apply the new memory allocation
            virsh --connect "$uri" setmem "$vm_name" "$new_memory"
        fi
    done
    
    # echo "waiting for next execution"
    
    [[ "$daemon" == "1" ]] && sleep 7
do true; done