You probably get some improvements of the file size when the migration
takes a while, depending on how much of the memory actually has to be
saved. You might however end up with a lot more small writes instead of
some big ones before, which might hurt performance.
Do you have any data about the resulting performance and file size?
ah, an important issue I haven't test, thanks for tipping it, let
me add code for migration to file, and have a test. It also
can be optimized a bit in qemu_fseek(), but IMHO the optimization
for small writes would better goto block layer either in qemu
or underling components in system.