Linux下清理記憶體和Cache方法 /proc/sys/vm/drop_caches

Linux下清理記憶體和Cache方法 /proc/sys/vm/drop_caches

頻繁的檔案訪問會導致系統的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記憶體減少到幾十兆，系統執行緩慢

執行sync將dirty的內容寫回硬碟
$sync

透過修改proc系統的drop_caches清理free的cache
$echo 3 > /proc/sys/vm/drop_caches

drop_caches的詳細文件如下：
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 新增如下選項後就不會記憶體持續增加
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

上面的設定比較粗暴，使cache的作用基本無法發揮。需要根據機器的狀況進行適當的調節尋找最佳的折衷。