图片移动、鼠标画线----实现GIS地图操作

摘自：http://rudd-o.com/linux-and-free-software/tales-from-responsivenessland-why-linux-feels-slow-and-how-to-fix-that
Tuning swappiness to prevent impromptu RAM hijacking
Swappiness is the name Linux kernel developers gave to the preference between paging applications
out to disk and (in practice) shrinking caches. If it's close to 0, Linux will prefer to keep applications
in RAM and not grow the caches. If it's close to 100, Linux will prefer to swap applications out, and
enlarge the caches as much as possible. The default is a halthy 6
调整交换分区的大小避免RAM使用到交换分区
交换分区实际上是Linux内核开发人员将进程中的页移到磁盘的一项技术。
如果关闭交换分区，Linux将所有的进程保存在RAM中，减少cache的使用
。如果交换分区接近100，Linux可能将进程换出RAM，尽可能的释放内存。
默认值是60.
The irony of this preference is that, in fact, paging an unused application out generally produces a net performance increment, since the cache really helps a lot when it's needed -- but this net performance increment translates to a net drop in perceived performance, since you usually don't care whether a file uncompresses a few seconds later, but you do care (a lot) when your applications don't respond instantaneously.
具有讽刺意味的是，被换出的进程产生一个性能上的提升，因为这个时候内存可以为所欲为。但是也带来性能上的问题，因为你可能不感兴趣保存在内存中的东西，什么玩意？但是你会耿耿于怀如果我的心肝宝贝没有响应。