@grips @romin @romin I don't remember this happening when I was using BuyVM's slabs, but I also had lvmcache in front of it that resided on the main disk. Still notifs wouldn't load half the time after a refresh.
I don't know how Postgres stores tables, but if it stores them in one giant file and that file is on the slab, it's entirely possible that slabs would be the issue. It could also be that CPU cores are stuck in iowait stalling everything else on the system.