linux 清内存

注意：首先我们需要使用sync指令，将所有未写的系统缓冲区写到磁盘中，包含已修改的 i-node、已延迟的块 I/O 和读写映射文件。否则在释放缓存的过程中，可能会丢失未保存的文件。

的值可以为0~3之间的任意数字，代表着不同的含义：

0 – 不释放

1 – 释放页缓存

2 – 释放dentries和inodes

3 – 释放所有缓存

[root@ok Desktop]# cat /proc/sys/vm/drop_caches
0
[root@ok Desktop]# file /proc/sys/vm/drop_caches
/proc/sys/vm/drop_caches: empty
[root@ok Desktop]# echo 1 >/proc/sys/vm/drop_caches
[root@ok Desktop]# free -h
total       used       free     shared    buffers     cached
Mem:           11G       966M        10G        53M       392K       161M
-/+ buffers/cache:       804M        10G
Swap:         3.6G         0B       3.6G

查看内存条个数:

[root@ok Desktop]# dmidecode | grep -A16 "Memory Device$"
Memory Device
Array Handle: 0x0005
Error Information Handle: Not Provided
Total Width: 64 bits
Data Width: 64 bits
Size: 8192 MB
Form Factor: SODIMM
Set: None
Locator: ChannelA-DIMM0
Bank Locator: BANK 0
Type: DDR3
Type Detail: Synchronous
Speed: 1600 MHz
Manufacturer: Kingston
Serial Number: 7633D911
Asset Tag: None
Part Number: KHX1600C9S3L/8G
--
Memory Device
Array Handle: 0x0005
Error Information Handle: Not Provided
Total Width: 64 bits
Data Width: 64 bits
Size: 4096 MB
Form Factor: SODIMM
Set: None
Locator: ChannelB-DIMM0
Bank Locator: BANK 2
Type: DDR3
Type Detail: Synchronous
Speed: 1600 MHz
Manufacturer: Samsung
Serial Number: 20A9C496
Asset Tag: None
Part Number: M471B5173DB0-YK0

清除pagecache:

[root@ok ~]# sync
[root@ok ~]# sysctl -w vm.drop_caches=1
vm.drop_caches = 1
[root@ok ~]# free -h
total       used       free     shared    buffers     cached
Mem:           11G       1.1G        10G        82M       412K       192M
-/+ buffers/cache:       980M        10G
Swap:         3.6G         0B       3.6G

清空 dentries 和 inodes：

[root@ok ~]# sync
[root@ok ~]# sysctl -w vm.drop_caches=2
vm.drop_caches = 2
[root@ok ~]# free -h
total       used       free     shared    buffers     cached
Mem:           11G       1.2G        10G        79M       5.7M       224M
-/+ buffers/cache:       959M        10G
Swap:         3.6G         0B       3.6G

清空所有缓存　pagecache、dentries 和 inodes）：

[root@ok ~]# sync
[root@ok ~]# sysctl -w vm.drop_caches=3
vm.drop_caches = 3
[root@ok ~]# free -h
total       used       free     shared    buffers     cached
Mem:           11G       1.1G        10G       101M       1.5M       210M
-/+ buffers/cache:       956M        10G
Swap:         3.6G         0B       3.6G