ionice não tem nenhum efeito em gravações não sincronizadas (isto é, gravações normais)?

Question

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.

Artem

Quando você grava dados no cache de páginas, não há campo para armazenar a prioridade de IO. Então ionice não terá efeito. Eu tenho isso certo?

Minha versão mais recente do kernel é 4.18.16-200.fc28.x86_64 .

    

Answer 1

Sim.

In theory, ionice allows you to prioritize a command's IO the way that nice(1) theoretically prioritizes its CPU usage. This would be a handy way to allow, say, a big but relatively important compile to grind away in the background without getting in the way of your interactive use of the machine.

(Why yes, I do recompile Firefox from source every so often.)

[...]

The next problem is that even when running directly on a disk, ionice does nothing to de-prioritize asynchronous write IO. This is, well, most of the write IO that most programs will do. Ionice may slow down synchronous writes (I don't have a test program) and it definitely works for reads, but that's it.

https://utcc.utoronto.ca/~cks/space/blog/linux/IoniceNotes