磁盘控制器是通过DMA来传输数据的？解决办法

磁盘控制器是通过DMA来传输数据的？
如果开启了O_DIRECT 磁盘控制器是通过DMA来传输数据的？
如果不是 就不是通过DMA方式了 而是采用缓存的方式

不知道 这样理解对不对？

C/C++ code

       O_DIRECT (Since Linux 2.4.10)

              Try to minimize cache effects of the I/O to and from this file.  In general this will degrade performance, but it is useful in special sit‐

              uations,  such  as when applications do their own caching.  File I/O is done directly to/from user space buffers.  The O_DIRECT flag on its

              own makes at an effort to transfer data synchronously, but does not give the guarantees of the O_SYNC that data and necessary metadata  are

              transferred.  To guarantee synchronous I/O the O_SYNC must be used in addition to O_DIRECT.  See NOTES below for further discussion.
              A semantically similar (but deprecated) interface for block devices is described in raw(8).




探讨
使用DMA的话 
linux的DMA是低端内存 也就那么点 给磁盘控制器使用 够用不？


楼上说的没错啦。
你说的磁盘缓存机制和DMA没有关系的。
现在一般的DMA应该都是支持32位地址了。
你说那个缓存是文件系统或者block驱动层的，
就算你block驱动层不使用缓存，到了下面的磁盘驱动里面哪里还是会使用DMA来进行的。