free -h

              total        used        free      shared  buff/cache   available
Mem:           7.7G        2.1G        3.2G        245M        2.4G        5.1G
Swap:          2.0G        0B          2.0G

swapon --show

NAME      TYPE SIZE USED PRIO
/dev/sda5 partition 2G   0B   -2

cat /proc/swaps

sudo fallocate -l 2G /swapfile

sudo dd if=/dev/zero of=/swapfile bs=1M count=2048

sudo chmod 600 /swapfile

sudo mkswap /swapfile

Setting up swapspace version 1, size = 2 GiB (2147479552 bytes)
no label, UUID=abcd1234-ef56-7890-abcd-ef1234567890

sudo swapon /swapfile

/swapfile none swap sw 0 0

# 1. 關(guān)閉當(dāng)前 Swap
sudo swapoff /swapfile

# 2. 刪除舊文件
sudo rm /swapfile

# 3. 創(chuàng)建新的更大文件
sudo fallocate -l 4G /swapfile

# 4. 設(shè)置權(quán)限
sudo chmod 600 /swapfile

# 5. 格式化
sudo mkswap /swapfile

# 6. 重新啟用
sudo swapon /swapfile

# 7. 驗(yàn)證
free -h

sudo truncate -s 4G /swapfile
sudo mkswap /swapfile
sudo swapon /swapfile

# 1. 關(guān)閉 Swap
sudo swapoff /swapfile

# 2. 重建較小的文件（例如 1GB）
sudo dd if=/dev/zero of=/swapfile bs=1M count=1024

# 3. 設(shè)置權(quán)限
sudo chmod 600 /swapfile

# 4. 格式化
sudo mkswap /swapfile

# 5. 啟用
sudo swapon /swapfile

swapon --show

NAME         TYPE      SIZE USED PRIO
/swapfile1   file      2G   0B   -2
/swapfile2   file      1G   0B   -1

sudo swapon -p 10 /swapfile

/swapfile none swap sw,pri=10 0 0

sudo swapoff /swapfile

sudo swapoff -a

sudo swapon -a

vmstat 1 5

procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu-----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa st
 1  0 102400 123456  78900 456789    0    0    12    34  100  200 10  5 85  0  0

sar -W 1 5

Linux 5.4.0-xx-generic (hostname)    04/01/2025      _x86_64_        (4 CPU)

03:00:01 PM  pswpin/s pswpout/s
03:00:02 PM      0.00      0.00
03:00:03 PM      0.00      0.00

import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
public class MemoryHog {
    private static List<byte[]> memoryChunks = new ArrayList<>();
    public static void main(String[] args) {
        System.out.println("?? Java Memory Hog 啟動(dòng)");
        System.out.println("本程序?qū)⒊掷m(xù)分配內(nèi)存，直到系統(tǒng)內(nèi)存耗盡或手動(dòng)停止。");
        System.out.println("按回車鍵開始分配內(nèi)存...");
        new Scanner(System.in).nextLine();
        int chunkSizeMB = 100; // 每次分配 100MB
        long totalAllocatedMB = 0;
        try {
            while (true) {
                byte[] chunk = new byte[chunkSizeMB * 1024 * 1024]; // 分配 100MB
                memoryChunks.add(chunk); // 保持引用防止 GC 回收
                totalAllocatedMB += chunkSizeMB;
                System.out.printf("? 已分配 %d MB 內(nèi)存\n", totalAllocatedMB);
                // 每次分配后稍作休眠，便于觀察系統(tǒng)狀態(tài)
                Thread.sleep(1000);
            }
        } catch (OutOfMemoryError e) {
            System.err.println("?? 發(fā)生 OutOfMemoryError！");
            System.err.println("堆內(nèi)存已耗盡。系統(tǒng)可能已開始使用 Swap 或終止進(jìn)程。");
            e.printStackTrace();
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
            System.out.println("?? 程序被中斷");
        }
    }
}

javac MemoryHog.java
java -Xmx4g MemoryHog  # 限制最大堆為 4GB

import java.io.BufferedReader;
import java.io.InputStreamReader;
public class SwapMonitor {
    public static void main(String[] args) throws Exception {
        System.out.println("?? 開始監(jiān)控 Swap 使用情況（每5秒刷新）");
        while (true) {
            SwapInfo info = getSwapInfo();
            System.out.printf(
                "?? %s | 總計(jì): %s | 已用: %s | 空閑: %s | 使用率: %.2f%%\n",
                java.time.LocalTime.now(),
                formatBytes(info.total),
                formatBytes(info.used),
                formatBytes(info.free),
                info.getUsagePercentage()
            );
            Thread.sleep(5000);
        }
    }
    public static SwapInfo getSwapInfo() throws Exception {
        Process process = Runtime.getRuntime().exec("free -b");
        BufferedReader reader = new BufferedReader(new InputStreamReader(process.getInputStream()));
        String line;
        while ((line = reader.readLine()) != null) {
            if (line.startsWith("Swap:")) {
                String[] parts = line.split("\\s+");
                long total = Long.parseLong(parts[1]);
                long used = Long.parseLong(parts[2]);
                long free = Long.parseLong(parts[3]);
                return new SwapInfo(total, used, free);
            }
        }
        throw new RuntimeException("未找到 Swap 信息");
    }
    private static String formatBytes(long bytes) {
        if (bytes < 1024) return bytes + " B";
        else if (bytes < 1024 * 1024) return String.format("%.2f KB", bytes / 1024.0);
        else if (bytes < 1024 * 1024 * 1024) return String.format("%.2f MB", bytes / (1024.0 * 1024));
        else return String.format("%.2f GB", bytes / (1024.0 * 1024 * 1024));
    }
    static class SwapInfo {
        final long total, used, free;
        SwapInfo(long total, long used, long free) {
            this.total = total;
            this.used = used;
            this.free = free;
        }
        double getUsagePercentage() {
            if (total == 0) return 0.0;
            return (used * 100.0) / total;
        }
    }
}

java \
  -Xms2g \           # 初始堆大小
  -Xmx2g \           # 最大堆大小
  -XX:MaxMetaspaceSize=512m \  # 元空間上限
  -XX:+UseG1GC \     # 使用 G1 垃圾回收器
  -XX:MaxGCPauseMillis=200 \   # 目標(biāo)最大 GC 暫停時(shí)間
  -XX:+AlwaysPreTouch \        # 啟動(dòng)時(shí)預(yù)分配并清零內(nèi)存頁，避免運(yùn)行時(shí)缺頁
  -XX:+DisableExplicitGC \     # 禁用 System.gc()
  -verbose:gc \                # 輸出 GC 日志
  -XX:+PrintGCDetails \
  -XX:+PrintGCTimeStamps \
  -Xloggc:/var/log/myapp-gc.log \
  -Djava.awt.headless=true \
  -jar myapp.jar

docker run \
  --memory="2g" \
  --memory-swap="2g" \   # 等于內(nèi)存 => 禁用 Swap
  --memory-swappiness=0 \ # 禁止容器使用 Swap
  my-java-app

apiVersion: v1
kind: Pod
metadata:
  name: java-app
spec:
  containers:
  - name: app
    image: my-java-image
    resources:
      limits:
        memory: "2Gi"
      requests:
        memory: "1.5Gi"

free -h

vmstat 1 5

for file in /proc/*/status ; do
    awk '/VmSwap|Name/{printf $2 " " $3}END{ print ""}' $file 2>/dev/null
done | sort -k 2 -n -r | head -10

java 102400 kB
mysqld 51200 kB
nginx 1024 kB

cat /proc/<PID>/smaps | grep -i swap

#!/bin/bash
# swap-manager.sh - 簡易 Swap 管理腳本
# 用法：./swap-manager.sh create 2G    # 創(chuàng)建 2GB Swap
#       ./swap-manager.sh resize 4G    # 調(diào)整為 4GB
#       ./swap-manager.sh remove       # 刪除 Swap
SWAPFILE="/swapfile"
FSTAB="/etc/fstab"
case "$1" in
    create)
        SIZE="$2"
        if [ -z "$SIZE" ]; then
            echo "? 請指定大小，如：2G"
            exit 1
        fi
        echo "?? 正在創(chuàng)建 $SIZE 的 Swap 文件..."
        sudo fallocate -l "$SIZE" "$SWAPFILE" || {
            echo "?? fallocate 失敗，嘗試使用 dd..."
            sudo dd if=/dev/zero of="$SWAPFILE" bs=1M count=$(echo "$SIZE" | sed 's/G/*1024/' | bc)
        }
        sudo chmod 600 "$SWAPFILE"
        sudo mkswap "$SWAPFILE"
        sudo swapon "$SWAPFILE"
        # 添加到 fstab
        if ! grep -q "$SWAPFILE" "$FSTAB"; then
            echo "$SWAPFILE none swap sw 0 0" | sudo tee -a "$FSTAB" > /dev/null
        fi
        echo "? Swap 已啟用：$(free -h | grep Swap)"
        ;;
    resize)
        SIZE="$2"
        if [ -z "$SIZE" ]; then
            echo "? 請指定新大小，如：4G"
            exit 1
        fi
        echo "?? 正在調(diào)整 Swap 大小至 $SIZE..."
        sudo swapoff "$SWAPFILE"
        sudo rm "$SWAPFILE"
        sudo fallocate -l "$SIZE" "$SWAPFILE" || {
            sudo dd if=/dev/zero of="$SWAPFILE" bs=1M count=$(echo "$SIZE" | sed 's/G/*1024/' | bc)
        }
        sudo chmod 600 "$SWAPFILE"
        sudo mkswap "$SWAPFILE"
        sudo swapon "$SWAPFILE"
        echo "? Swap 已調(diào)整：$(free -h | grep Swap)"
        ;;
    remove)
        echo "???  正在移除 Swap..."
        sudo swapoff "$SWAPFILE"
        sudo rm "$SWAPFILE"
        # 從 fstab 中刪除
        sudo sed -i "\|^$SWAPFILE|d" "$FSTAB"
        echo "? Swap 已移除"
        ;;
    *)
        echo "用法：$0 {create|resize|remove} [size]"
        echo "示例："
        echo "  $0 create 2G"
        echo "  $0 resize 4G"
        echo "  $0 remove"
        ;;
esac

chmod +x swap-manager.sh