Linux下清理内存和Cache方法

频繁的文件访问会导致系统的Cache使用量大增
$ free -m
             total       used       free     shared    buffers     cached
Mem:          8054       5008       3045          0        364       1218
-/+ buffers/cache:       3426       4627
Swap:         4102          5       4097

free内存减少到几十兆，系统运行缓慢
运行sync将dirty的内容写回硬盘
$sync

通过修改proc系统的drop_caches清理free的cache
$echo 3 > /proc/sys/vm/drop_caches

drop_caches的详细文档如下：
Writing to this will cause the kernel to drop clean caches, dentries and inodes from memory, causing that memory to become free.
To free pagecache:
* echo 1 > /proc/sys/vm/drop_caches
To free dentries and inodes:
* echo 2 > /proc/sys/vm/drop_caches
To free pagecache, dentries and inodes:
* echo 3 > /proc/sys/vm/drop_caches
As this is a non-destructive operation, and dirty objects are notfreeable, the user should run "sync" first in order to make sure allcached objects are freed.
This tunable was added in 2.6.16.

修改/etc/sysctl.conf 添加如下选项后就不会内存持续增加
vm.dirty_ratio = 1
vm.dirty_background_ratio=1
vm.dirty_writeback_centisecs=2
vm.dirty_expire_centisecs=3
vm.drop_caches=3
vm.swappiness =100
vm.vfs_cache_pressure=163
vm.overcommit_memory=2
vm.lowmem_reserve_ratio=32 32 8
kern.maxvnodes=3