GC stall in luaC_separateudata

[Niklas Frykholm <niklas@...>]

I am seeing a GC stall of about 8 ms in luaC_separateudata(). After 
looking at the code and reading chapter 31 of Programming in Lua, I 
think that there simply are too many userdata objects in my lua state.
I have about 130 000 userdata objects. The reason for that insane ammout 
is that I am simulating a big world and many of the C/C++ objects are 
mirrored on the Lua side as userdata.
My plan now is to reduce the number of "mirrored" objects by rewriting 
the structures so that Lua doesn't keep a live reference to everything 
on the C side, but instead just fetches the references it needs to work 
on from C and then releases them.
Since this might be a significant rewrite I just thought I should ask 
first if anyone else has encountered this problem or has any other ideas 
on how to address it.
// Niklas