In article <5l90zjv417.fsf@tequila.systemsz.cs.yale.edu> you write:
>Felix Schroeter <felix@mamba.pond.sub.org> writes:
>> Does that mean, if you have a 1GB real mem machine, there's 1GB of virtual
>> memory already used for a permanent mapping of the real 1GB of memory?
>Exactly.
>But it's really not a big deal since it's only "virtual memory"
>which only costs a few page-table entries (and no swap).
It costs 1GB/1024 = 1MB for the PTEs. And it causes that no user processes
can ever have more than 3GB of VM (in fact a bit less, because the kernel
needs its own VM in addition to the physmem mapping). On systems without
such a permanent mapping, you had a bit less than 4 GB for the VM.
Regards, Felix.