Linux Process status D

The DVR is configured with a m clock speed of arm11 and M memory, half of which are allocated to the video decoder. The kernel and other processes also occupy a lot of memory, leaving less memory for Qt to run. Later, we transplanted QT browser and QT WebKit to the DVR for map display. Although some functions have been cropped out, the running is still very card, and the QT interface process is easy to enter the State D. Then, it will take a while to buffer the data.

Know the status D on the network. That is to say: if the requested Io resources cannot be met, wait for the status D.
In this project, we killed another process and left some memory for Qt. Then, the situation immediately eased. After testing for a while, we didn't get stuck in status D. This indicates that memory is also a factor affecting status D.
What is the relationship between memory and I/O resources that will link the memory with the Process status?