Linux下清理内存和Cache方法 /proc/sys/vm/drop_caches
频繁的文件訪问会导致系统的Cache使用量大增
$ free -m
total used free shared buffers cached
Mem: 3955 3926 28 0 55 3459
-/+ buffers/cache: 411 3544
Swap: 5726 0 5726
free内存降低到几十兆，系统执行缓慢
执行sync将dirty的内容写回硬盘
$sync
通过改动proc系统的drop_caches清理free的cache
$echo 3 > /proc/sys/vm/drop_caches
drop_caches的具体文档例如以下：
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.
改动/etc/sysctl.conf 加入例如以下选项后就不会内存持续添加
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
上面的设置比較粗暴，使cache的作用基本无法发挥。
须要依据机器的状况进行适当的调节寻找最佳的折衷。