Question on "mappings as cache"

Jonathan S. Shapiro shap at
Sun Dec 7 18:46:54 CET 2003

I am trying to understand the implications of the "mapping is a cache"
design argument. I suspect that this design can only be upheld if
encapsulation is violated. First, however, I would like to understand
the sequence of events in the following scenario:

Consider a situation in which

   A maps some region to B
   B completes the receive operation, and therefore
     now has a copy of the mapping
   B is immediately preempted, before it can do any user-level
     book keeping about the mapping
   ... other stuff runs ...
   kernel runs out of mapping cache space, chooses to evict
     the mapping just received by B
   ... other stuff runs ...
   B attempts to reference the region that it believes should
     be mapped, and page faults.

Can someone explain the process by which B is able to get the mapping


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