手动释放内存

1. free -m

2. sync

3. echo 3 > /proc/sys/vm/drop_caches

关于drop_caches的官方说明如下：

　　Writing to this file causes the kernel to drop clean caches,dentries and inodes from memory, causing that memory to becomefree.

　　To free pagecache, use echo 1 > /proc/sys/vm/drop_caches;

　　to free dentries and inodes, use echo 2 > /proc/sys/vm/drop_caches;

　　to free pagecache, dentries and inodes, use echo 3 >/proc/sys/vm/drop_caches.

　　Because this is a non-destructive operation and dirty objects are not freeable, the user should run sync first.