Adjust memory "slop" associated with a vnode host.
We hit a scenario where we were using 126GB of RAM on a shared d820 vnode host (117GB for vnodes, 8GB for dom0 and 1GB "slop") leaving 2GB for additional vnodes. Someone tried to start 2 x 1GB vnodes, which both mapped to that host, but the second one failed to start with xl create
complaining that it ran out of memory for the domU's "reserved memory". So perhaps 1GB is not enough "slop"? Given that d710
s only have 12GB of physical RAM, lopping off another 0.5 to 1GB is a significant hit. But maybe we don't care about d710
s as vnode hosts anymore.