I have a 30GB file on an SSD disk and a process that continuously in a loop reads and writes from/to random locations in the file.
According to IO top, the process consumes almost max read and write IO (40MB/s read, 120MB/s writes, ~95% IO) for ~30 seconds. During those 30 seconds no other process shows any usage of the IO. During that time, while total IO is showing ~120M/s, the actual IO appears to be idle.
Then after 30 seconds kworker appears on top. It shows 0 DISK READ and 0 DISK WRITE, but ~95% IO. It lasts for ~45 seconds, and during those 45 seconds my process also shows ~95% IO, but the read and write speed goes down significantly, to around 2MB/s and 6MBs correspondingly, with high variance. The total IO during this period is close to zero, but the actual IO is now high. After ~45 seconds, kworker disappears, and my process runs at full speed for another 30 seconds.
What is the likely cause of this behavior?
