手动释放内存
1.sync将内存中的缓存写入磁盘
2. 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.
Linux手动释放内存
原文：http://www.cnblogs.com/tla001/p/6205079.html
