#!/bin/bash

########
# zswap-stats
# version: 2023-06-09.1
#
# Licence: CC-BY-SA 4.0
# https://wiki.tnonline.net
########

# System page size
page_size=$(getconf PAGESIZE)

# Location of zswap settings
settings_dir="/sys/module/zswap/parameters"

# Location of zswap statistics
statistics_dir="/sys/kernel/debug/zswap"

# Array of zswap settings
settings=("accept_threshold_percent" "compressor" "enabled" "max_pool_percent" "non_same_filled_pages_enabled" "same_filled_pages_enabled" "zpool")

# Array of zswap statistics
statistics=("duplicate_entry" "pool_limit_hit" "pool_total_size" "reject_alloc_fail" "reject_compress_poor" "reject_kmemcache_fail" "reject_reclaim_fail" "same_filled_pages" "stored_pages")

# Declare an associative array to store zswap data
declare -A zswap_data

# Read zswap settings
for setting in "${settings[@]}"; do
	read -r value < "$settings_dir/$setting"
	zswap_data["$setting"]=$value
done

# Read zswap statistics
for stat in "${statistics[@]}"; do
	read -r value < "$statistics_dir/$stat"
	zswap_data["$stat"]=$value
done

# Determine the maximum length of variable names
max_length=0
for key in "${!zswap_data[@]}"; do
	if [ ${#key} -gt $max_length ]; then
		max_length=${#key}
	fi
done
((width = max_length + 4))

# Calculate the total size and compressed size in MiB
total_size=$((zswap_data["stored_pages"] * page_size / (1024 * 1024) ))
compressed_size=$((zswap_data["pool_total_size"] / (1024 * 1024) ))

# Calculate the compression ratio
if [ "${zswap_data["stored_pages"]}" -ne 0 ]; then
	compression_ratio=$(bc <<< "scale=2; (${zswap_data["stored_pages"]} * $page_size / ${zswap_data["pool_total_size"]})")
else
	compression_ratio=0
fi

# Output the zswap settings
printf "========\n"
printf "SETTINGS"
printf "\n========\n"
for key in "${settings[@]}"; do
    # Get the value from the associative array
    value=${zswap_data["$key"]}

    # Output the key (name) and value in columns
    printf "%-*s%s\n" "$width" "$key" "$value"
done

# Output the zswap data
printf "\n========\n"
printf "VALUES"
printf "\n========\n"
for key in "${statistics[@]}"; do
    # Get the value from the associative array
    value=${zswap_data["$key"]}

    # Output the key (name) and value in columns
    printf "%-*s%s\n" "$width" "$key" "$value"
done

# Output the total size, compressed size, and compression ratio
printf "\n========\n"
printf "SUMMARY"
printf "\n========\n"
printf "%-*s%s MiB\n" "$width" "Total Size:"        "$total_size"
printf "%-*s%s MiB\n" "$width" "Compressed Size:"   "$compressed_size"
printf "%-*s%s\n"     "$width" "Compression Ratio:" "$compression_ratio"