cached是作为page cache的内存, 文件系统的cache。你读写文件的时候，Linux内核为了提高读写机能与速度，昆山软件公司，会将文件在内存中举办缓存，这部门内存就是Cache Memory(缓存内存)。纵然你的措施运行竣事后，Cache Memory也不会自动释放。这就会导致你在Linux系统中措施频繁读写文件后，你会发明可用物理内存会很少。其实这缓存内存(Cache Memory)在你需要利用内存的时候会自动释放，所以你不必担忧没有内存可用

Cached is the size of the page cache. Buffers is the size of in-memory block I/O buffers. Cached matters; Buffers is largely irrelevant.

Cached is the size of the Linux page cache, minus the memory in the swap cache, which is represented by SwapCached (thus the total page cache size is Cached + SwapCached). Linux performs all file I/O through the page cache. Writes are implemented as simply marking as dirty the corresponding pages in the page cache; the flusher threads then periodically write back to disk any dirty pages. Reads are implemented by returning the data from the page cache; if the data is not yet in the cache, it is first populated. On a modern Linux system, Cached can easily be several gigabytes. It will shrink only in response to memory pressure. The system will purge the page cache along with swapping data out to disk to make available more memory as needed.

Buffers are in-memory block I/O buffers. They are relatively short-lived. Prior to Linux kernel version 2.4, Linux had separate page and buffer caches. Since 2.4, the page and buffer cache are unified and Buffers is raw disk blocks not represented in the page cache—i.e., not file data. The Buffers metric is thus of minimal importance. On most systems, Buffers is often only tens of megabytes. 

Linux共享内存

共享内存是历程间通信中最简朴的方法之一。共享内存答允两个或更多历程会见同一块内存，就如同 malloc() 函数向差异历程返回了指向同一个物理内存区域的指针。当一个历程改变了这块地点中的内容的时候，其它历程城市察觉到这个。其实所谓共享内存，就是多个历程间配合地利用同一段物理内存空间，它是通过将同一段物理内存映射到差异历程的虚拟空间来实现的。由于映射到差异历程的虚拟空间中，差异历程可以直接利用，不需要像动静行列那样举办复制，所以共享内存的效率很高。共享内存可以通过mmap()映射普通文件机制来实现，也可以System V共享内存机制来实现，System V是通过映射非凡文件系统shm中的文件实现历程间的共享内存通信，也就是说每个共享内存区域对应非凡文件系统shm中的一个文件。