After installing windows 2008 R2 sp1 RTM, I can't wait to change the memory mode from "static" to "dynamic". Previously, one of my virtual machine was allocated 2048 MB RAM, so I specified "1024 MB" to the "Startup RAM", and the "Maximum RAM" is set to "6144 MB" (physical memory on the host machine is 8 GB). However, I was quite surprised to see that the guest machine became very slow, then hard disk indicator light was going crazy, and its disk queue increased to 50 immediately after rebooting!
Here explains what happened. Guest OS needs to notify host OS when it needs more or less memory, and the only way of the communication is through "integration components (service)".
So, what we need to do is quite easy: Upgrade "integration components (service)" to SP1 from the guest OS.
PS: May need to shut down all virtual machines, then reboot the three Hyper-V windows services on the host machine after the upgrading.
Update (6, March, 2011):
From here, I realized that dynamic memory may not work well because normally developers would choose "SQL Server developer edition". This is described as below:
"Only certain version and editions of SQL Server have the capability to recognised hot-add memory -Only Enterprise and DataCenter editions for SQL Server 2005 and later."