Yes, at some point I got a report about Xen 3.0 (If I remember correctly) fixing the issue, but I never see in the real world things improving much AFAIK. Here is a table that shows fork times with different environments, just to show how bad the thing is:

Linux beefy VM on VMware 6.0GB: 12.8 milliseconds per GB.

Linux running on physical machine (Unknown HW): 13.1 milliseconds per GB.

Linux running on physical machine (Xeon @ 2.27Ghz): 9 milliseconds per GB.

Linux VM on 6sync (KVM): 23.3 millisecond per GB.

Linux VM on EC2 (Xen): 239.3 milliseconds per GB.

Linux VM on Linode (Xen): 424 milliseconds per GB.

Around 30 times slower than bare metal, and I'm talking about old physical servers with slow memory compared to today's.

EDIT: Make sure to read this -> https://redislabs.com/blog/testing-fork-time-on-awsxen-infra...

Have you tried to use huge page to reduce the time of fork()?

There also a similar problem for master of MFS, it will be great if you have some experience in it.

EDIT: https://www.kernel.org/doc/Documentation/vm/hugetlbpage.txt

At least one user of Redis tried to enable huge pages and reported that there were issues: https://groups.google.com/d/msg/redis-db/3VCDYKXhDdI/rIaPnK9...