Linux下清理內存和Cache方法

頻繁的文件訪問會致使系統的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內存減小到幾十兆，系統運行緩慢

（1）運行sync將dirty的內容寫回硬盤

$sync

經過修改proc系統的drop_caches清理free的cache

$echo 3 > /proc/sys/vm/drop_caches

drop_caches的詳細文檔以下：

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.

（2）修改/etc/sysctl.conf 添加以下選項後就不會內存持續增長

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

上面的設置比較粗暴，使cache的做用基本沒法發揮。須要根據機器的情況進行適當的調節尋找最佳的折衷