Comment 205 for bug 1518457

> Problem, causes always heavy kswapd0 load:
> cat /dev/sda >> /dev/zero
> hdparm -t /dev/sda
> ddrescue /dev/sda /dev/zero -vf
> hexdump /dev/sda
> dd if=/dev/sda of=/dev/zero
> etc.

of course those cause kswapd work, all those commands will fill your page cache and kswapd is responsible for clearing those pages out.

kswapd running isn't a problem, if it's doing work. kswapd running *without* doing work is the problem. When you stop running those commands, does kswapd catch up and stop using cpu? If so, that's normal. If not, and it never stops using cpu, that's the problem.

> No problem (read speed ~500MB/s, except hdparm ):
> hdparm --direct -t /dev/sda
> dd iflag=direct if=/dev/sda of=/dev/zero bs=1073741824
> ddrescue --direct /dev/sda /dev/zero -vf -b 4096 -c 8192

the difference is those commands bypass the page cache - so the page cache doesn't fill up and kswapd doesn't need to clear it out.