Linux Swap 启停及swappiness设置

生成swap分区

可以通过磁盘分区和文件两种方式进行操作

1. 通过磁盘分区

• 划出一块4G磁盘fdisk /dev/sdb
  

  sdb磁盘对应的文件

[root@centosgpt ~]# fdisk /dev/sdb
Command (m for help): n
Partition number (1-128, default 1):
First sector (34-41943006, default 2048):
Last sector, +sectors or +size{K,M,G,T,P} (2048-41943006, default 41943006): +4G
Created partition 1
...
Command (m for help): p
...
#         Start          End    Size  Type            Name
 1         2048      8390655      4G  Linux filesyste
 ..
Command (m for help): w
The partition table has been altered!

• 创建分区mkswap /dev/sdb1
  

  sdb1对应分区

[root@centosgpt ~]# mkswap /dev/sdb1
Setting up swapspace version 1, size = 1020 KiB
no label, UUID=5dabc5b1-d763-4757-9e0c-383f0cacb0ea

2. 通过文件生成

• 生成文件dd if=/dev/zero of=/swap bs=1MB count=1024
  

  bs 以1M为单位, count多少个1MB块

[root@centosgpt ~]# dd if=/dev/zero of=/swap bs=1MB count=1024
1024+0 records in
1024+0 records out
1024000000 bytes (1.0 GB) copied, 1.36373 s, 751 MB/s

• 赋予权限chown root:root /swap
  chmod 600 /swap

[root@centosgpt ~]# chown root:root /swap
[root@centosgpt ~]# chmod 600 /swap

• 创建分区
  mkswap -L swap /swap

[root@centosgpt ~]# mkswap -L swap /swap
Setting up swapspace version 1, size = 999996 KiB
LABEL=swap, UUID=e382380e-c729-40e6-bf3b-823d5cd9b55f

3. 通过LVM2创建

1. Create the LVM2 logical volume of size 2 GB:
# lvcreate VolGroup00 -n LogVol02 -L 2G
2. Format the new swap space:
# mkswap /dev/VolGroup00/LogVol02

https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/storage_administration_guide/ch-swapspace

开启关闭swap分区

1.开启分区

swapon -s

[root@centosgpt ~]# swapon -s
Filename                                Type            Size    Used    Priority
/dev/dm-1                               partition       4194300 0       -2
[root@centosgpt ~]# swapon /dev/sdb1
[root@centosgpt ~]# swapon -s
Filename                                Type            Size    Used    Priority
/dev/dm-1                               partition       4194300 0       -2
/dev/sdb1                               partition       1020    0       -3

2 永久生效

/etc/fstab

[root@centosgpt ~]# cat /etc/fstab |grep swap
/dev/mapper/centos-swap swap    swap    defaults        0 0
/dev/sdb1 none swap sw 0 0

3.关闭分区

swapoff

[root@centosgpt ~]# swapon
NAME      TYPE        SIZE USED PRIO
/swap     file      976.6M   0B   -2
/dev/sdb1 partition  1020K   0B   -3
/dev/dm-1 partition     4G   0B   -4
[root@centosgpt ~]# swapoff /swap
[root@centosgpt ~]# swapon
NAME      TYPE       SIZE USED PRIO
/dev/sdb1 partition 1020K   0B   -2
/dev/dm-1 partition    4G   0B   -3
[root@centosgpt ~]# swapoff /dev/sdb1
[root@centosgpt ~]# swapon
NAME      TYPE      SIZE USED PRIO
/dev/dm-1 partition   4G   0B   -2

swappiness参数

swappiness参数指导如何使用swap分区, 值越小越偏向使用物理内存， 越大越趋向使用swap分区.

1. 查看

[root@centosgpt ~]# sysctl -n vm.swappiness
30

cat /proc/sys/vm/swappiness

1. 临时调整

sysctl vm.swappiness=40

2. 永久调整

/etc/sysctl.conf
vm.swappiness = 10
sysctl -p 

参考引用

Linux交换空间（swap space）的那些优缺点
Linux 创建交换（swap）分区