NetBSD Project: Auto create swap on memory pressure

#!/bin/bash

# Configurable parameters
MAX_SWAP_SIZE=80                # Max space usage as percentage of disk
MIN_FREE_SPACE=10               # Minimum free space percentage on disk
MEMORY_THRESHOLD=80             # Memory usage threshold for swap creation
SWAP_FILE="/swapfile"           # Swap file location
LOG_FILE="/var/log/swap_manager.log"  # Log file location
SWAP_SIZE_INCREMENT=1024        # Size increment for swap file (in MB)
THROTTLE_TIMEOUT=300            # Timeout in seconds between swap creations (5 minutes)

# Log function
log_message() {
    local message=$1
    local current_time=$(date '+%Y-%m-%d %H:%M:%S')
    echo "$current_time - $message" >> $LOG_FILE
}

# Monitor and create swap file if needed
create_swap() {
    log_message "Checking disk and memory usage..."

    # Get disk space usage and free memory
    FREE_SPACE=$(df / | awk 'NR==2 {print $5}' | sed 's/%//')
    FREE_MEMORY=$(vmstat -s | grep "free memory" | awk '{print $1}')
    TOTAL_MEMORY=$(sysctl -n hw.physmem)
    AVAILABLE_MEMORY=$(($TOTAL_MEMORY - $FREE_MEMORY))

    # Check if enough disk space is available
    if [ "$FREE_SPACE" -ge "$MAX_SWAP_SIZE" ]; then
        log_message "Disk space is too low. Swap creation aborted."
        return 1
    fi

    # Check if memory usage exceeds the threshold
    if [ $(($AVAILABLE_MEMORY * 100 / $TOTAL_MEMORY)) -ge "$MEMORY_THRESHOLD" ]; then
        log_message "Memory usage is above threshold, creating swap file..."
        
        # Dynamically calculate swap file size based on memory usage (1 GB per 10% memory usage above threshold)
        SWAP_SIZE=$((($AVAILABLE_MEMORY * 100 / $TOTAL_MEMORY - $MEMORY_THRESHOLD) * $SWAP_SIZE_INCREMENT / 10))
        if [ "$SWAP_SIZE" -lt "$SWAP_SIZE_INCREMENT" ]; then
            SWAP_SIZE=$SWAP_SIZE_INCREMENT
        fi

        # Check if a swap file already exists, remove it
        if [ -f $SWAP_FILE ]; then
            log_message "Swap file $SWAP_FILE exists. Removing existing swap file..."
            swapoff $SWAP_FILE
            rm -f $SWAP_FILE
        fi
        
        # Create swap file and set up swap
        dd if=/dev/zero of=$SWAP_FILE bs=1M count=$SWAP_SIZE status=progress
        mkswap $SWAP_FILE
        swapon $SWAP_FILE
        log_message "Created swap file of size $SWAP_SIZE MB at $SWAP_FILE."
    else
        log_message "Memory usage below threshold, no swap file needed."
    fi
}

# Remove swap file if memory usage is low
remove_swap() {
    # Check if swap file is in use
    SWAP_USAGE=$(swapon -s | grep $SWAP_FILE)
    if [ -z "$SWAP_USAGE" ]; then
        log_message "No swap file in use. Cleanup skipped."
    else
        log_message "Memory usage has decreased. Removing swap file..."
        swapoff $SWAP_FILE
        rm -f $SWAP_FILE
        log_message "Removed swap file $SWAP_FILE."
    fi
}

# Check disk space before proceeding
check_disk_space() {
    DISK_USAGE=$(df / | awk 'NR==2 {print $5}' | sed 's/%//')
    if [ "$DISK_USAGE" -ge "$MAX_SWAP_SIZE" ]; then
        log_message "Disk usage too high ($DISK_USAGE%). Aborting swap file creation."
        return 1
    fi
    return 0
}

# Rate limiting for swap file creation to avoid thrashing
throttle_check() {
    last_creation=$(stat -c %Y $LOG_FILE)
    current_time=$(date +%s)
    elapsed_time=$((current_time - last_creation))
    if [ "$elapsed_time" -lt "$THROTTLE_TIMEOUT" ]; then
        log_message "Throttling swap creation. Elapsed time: $elapsed_time seconds."
        return 1
    fi
    return 0
}

# Main control loop for swap management
manage_swap() {
    log_message "Starting swap management..."

    # Check disk space and memory, and create swap if necessary
    if check_disk_space && throttle_check; then
        create_swap
    else
        log_message "Swap creation skipped due to insufficient disk space or throttling."
    fi

    # Optionally, clean up swap if memory usage is back to normal
    remove_swap
}

# Run the script
manage_swap