Comment 58 for bug 1861359

Sultan, thanks for the advice.

I set this watermark boost factor to zero as you suggested, and then decided to try a stupid simple benchmark of my storage -- my swap is a zfs dataset on nvme. zfs means it'll go slower than raw nvme block access:

$ dd if=ubuntu-18.04.4-desktop-amd64.iso of=foo bs=$((1024*1024)) conv=fsync
2028+1 records in
2028+1 records out
2126544896 bytes (2.1 GB, 2.0 GiB) copied, 6.91399 s, 308 MB/s

And this is a sequential workload with large blocks rather than random with pages, but it gives the flavour of the speed well enough.

Anyway, my system hung again when re-focusing firefox even after changing the watermark boost factor to zero. It was unusable for ten or twenty seconds. I have loads of free memory, it shouldn't be in swap:

$ free -h
              total used free shared buff/cache available
Mem: 15Gi 11Gi 1.6Gi 643Mi 2.2Gi 2.8Gi
Swap: 2.0Gi 23Mi 2.0Gi

Thanks