On Mon, Sep 20, 2021 at 09:54:31AM +0100, Mel Gorman wrote:

This has been lightly tested only and the testing was useless as the
relevant code was not executed. The workload configurations I had that
used to trigger these corner cases no longer work (yey?) and I'll need
to implement a new synthetic workload. If someone is aware of a realistic
workload that forces reclaim activity to the point where reclaim stalls
then kindly share the details.

The stereeotypical "stalling on I/O" problem is to plug in one of the
crap USB drives you were given at a trade show and simply
	dd if=/dev/zero of=/dev/sdb
	sync

You can also set up qemu to have extremely slow I/O performance:
https://serverfault.com/questions/675704/extremely-slow-qemu-storage-performance-with-qcow2-images