/proc是個虛擬文檔系統,我們能夠通過對他的讀寫操作做為和kernel實體間進行通信的一種手段.也就是說能夠通過修改/proc中的文檔,來對當前kernel的行為做出調整.那么我們能夠通過調整/proc/sys/vm/drop_caches來釋放內存.操作如下:

[root@server test]# cat /proc/sys/vm/drop_caches
0

首先,/proc/sys/vm/drop_caches的值,默認為0

[root@server test]# sync

手動執行sync命令(描述:sync 命令運行 sync 子例程。假如必須停止系統，則運行 sync 命令以確保文檔系統的完整性。sync 命令將任何未寫的系統緩沖區寫到磁盤中，包含已修改的 i-node、已延遲的塊 I/O 和讀寫映射文檔)

[root@server test]# echo 3 > /proc/sys/vm/drop_caches
[root@server test]# cat /proc/sys/vm/drop_caches
3

將/proc/sys/vm/drop_caches值設為3

[root@server test]# free -m
total used free shared buffers cached
Mem: 249 66 182 0 0 11
-/+ buffers/cache: 55 194
Swap: 511 0 511

再來運行free命令,發現現在的used為66MB,free為182MB,buffers為0MB,cached為11MB.那么有效的釋放了buffer和cache.

有關/proc/sys/vm/drop_caches的用法在下面進行了說明

/proc/sys/vm/drop_caches (since Linux 2.6.16)
Writing to this file causes the kernel to drop clean caches,
dentries and inodes from memory, causing that memory to become
free.
To free pagecache, use echo 1 > /proc/sys/vm/drop_caches; to
free dentries and inodes, use echo 2 > /proc/sys/vm/drop_caches;
to free pagecache, dentries and inodes, use echo 3 >
/proc/sys/vm/drop_caches.
Because this is a non-destructive operation and dirty objects
are not freeable, the user should run sync(8) first.