Great question — answering as the UphillTech team:
With memory ballooning enabled, the minimum is not guaranteed, but rather it is the balloon target, a wager that there will be memory available. Proxmox auto balloon may reduce below this minimum, if the host has memory pressure or is above 80% utilized and the other guests are not reclaiming enough. Catastrophically bad performance of everything on the host, and out of memory conditions in the guests, is a risk of overprovisioning memory. First, some conservative capacity planning. Subtract at least 1 GB from the host physical memory, to reserve for the host. The remainder is the budget for your VMs and containers. Then set less ambitious memory allocations on VM guests, with a smaller...
Full answer by John Mahowald: https://superuser.stackexchange.com/a/1940846 (CC BY-SA 4.0).
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