> Could you collect /proc/vmstat every second or so while you observe this
behavior? This should give us more information that vmstat(8) output.

Hi Michal,

Thanks for the suggestion - I've re-run the test on a 5.5.0-rc6 kernel built from source using the default config, which exhibits the same behaviour. Please see attachment; I hope the format is OK.

Here's the timeline of events:
18:25:00	start
18:25:10	run `stress` to limit available memory (grabs 0.9 x MemAvailable)
18:25:20	run `dd` to exercise the buffer cache
18:26:00	echo 3 > /proc/sys/vm/drop_caches
18:26:30	echo 3 > /proc/sys/vm/drop_caches

The paging stops after each drop_caches, but starts again once the buffer cache utilisation rises.

Best regards,
Chris