linux如何释放cache

[root@master ~]# free -m
             total       used       free     shared    buffers     cached
Mem:          2009       1999          9          0       1308        437
-/+ buffers/cache:        253       1756
Swap:         5951          0       5951

[root@master ~]# cat /proc/sys/vm/drop_caches 
0
[root@master ~]# echo 3 > /proc/sys/vm/drop_caches 

[root@master ~]# cat /proc/sys/vm/drop_caches 
3
[root@master ~]# sync
[root@master ~]# free -m
             total       used       free     shared    buffers     cached
Mem:          2009        463       1545          0        176         49
-/+ buffers/cache:        236       1772
Swap:         5951          0       5951

有关/proc/sys/vm/drop_caches的用法在下面进行了说明


/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.