When I dump a large MySQL database (its dump weighs around 10GB) - it appears on the disk almost immediately, but then, later, when the kernel decides to flush it to the disk, the server almost stalls and other IO requests take a lot more time to complete even though mysqldump is run with ionice -c3, so the use of ionice has no real effect.
When you write data into the page cache, there is no field to store the IO priority. So
ionice will have no effect. Do I have that right?
My latest kernel version is