Linux下清理內存和Cache方法 /proc/sys/vm/drop_caches

頻繁的文件訪問會導致系統的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內存減少到幾十兆，系統運行緩慢

運行sync將dirty的內容寫回硬盤
$sync

通過修改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 添加如下選項后就不會內存持續增加

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

上面的設置比較粗暴，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。

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