Re: [Qemu-devel] coroutines and block I/O considerations

[Paolo Bonzini]

On 07/19/2011 12:57 PM, Stefan Hajnoczi wrote:
>  From what I understand "committed" on Windows means that physical
> pages have been allocated and pagefile space has been set aside:
> http://msdn.microsoft.com/en-us/library/ms810627.aspx

Yes, memory that is "reserved" on Windows is just a contiguous part of 
the address space that is set aside, like MAP_NORESERVE under Linux. 
Memory that is "committed" is really allocated.

> The question is how can we get the same effect on Windows and does the
> current Fibers implementation not already work?

Windows thread and fiber stacks have both a reserved and a committed 
part.  The dwStackSize argument to CreateFiber indeed represents 
_committed_ stack size, so we're now committing 4 MB of stack per fiber. 
 The maximum size that the stack can grow to is set to the 
(per-executable) default.

If you want to specify both the reserved and committed stack sizes, you 
can do that with CreateFiberEx.

http://msdn.microsoft.com/en-us/library/ms682406%28v=vs.85%29.aspx

4 MB is quite a lot of address space anyway to waste for a thread.  A 
coroutine should not need that much, even on Linux.  I think for Windows 
64 KB of initial stack size and 1 MB of maximum size should do (for 
Linux it would 1 MB overall).

Paolo