RE: Sawmill's dataspaces and the Hurd's physmem

[yuan Darwin-r62832]

Hi Neal,

        I think these 2 approachs are not incompatible. Here are the reasons,

        1. In Hurd's approach, every application could manage its own physical 
memory. However, for most of application developers, they don't want to take 
care of the VM replacement policy. To solve this problem, Hurd has to provide a 
general VM server to be the pager of this kind of applications. However, as the 
philosophy of Hurd, should this applications trust this server?

        2. In Sawmill's DS approach, every task(AS) has a specific thread named 
"region mapper" to be the pager of other threads. It captures the page fault, 
then decide to forward it to corresponding server, and get mapped. So from the 
higher level point of view, these servers are the pagers of the task. If Hurd 
application should trust that general VM pager, the applications using 
Sawmill's DS framework should trust these servers as well.

        3. Relative to Sawmill's approach, Hurd provides a clear & great 
physical memory server, which makes the whole physical memory of platform could 
be fairly used by all of the servers & applications. 

        Therefore, we can use Hurd's physmem server as the central controller. 
Sawmill's DSMs apply physical memory from it. The applications who wanna use 
Sawmill's approach could still walk on their own way. For some applications who 
wanna manage their own physical memory, they can apply memory from physmem 
server directly.

                      [ physmem ]
                       /           \
                     |_           _|
                [ DSM ]      [Hurd app] (manage physmem by itself]
              /      \
            |_        _|
  [Sawmill app]  [Sawmill app]

Best Regards,
Darwin