vshost and /3GB problem

Yesterday I found that if you debug a process in Visual Studio 2008 on a machine with /3GB enabled, then the Visual Studio Hosting Process (on by default in the debug properties pane) will annoyingly reserve a 1gig chunk of memory for itself. This cancels out any benefit you hope to acquire by running with a 3gig address space!

I don’t know why. But in the meantime, I’ve turned off this hosting option in the Prost8 vcproject file.

Just because it’s fun to see:

From output !sos.vmmap:

...
7fffe000-7fffefff 00001000 RdWr RdWr Commit Private
7ffff000-7fffffff 00001000 RdWr RdWr Commit Private
80000000-bffdffff 3ffe0000 Rd Reserve Private (that is a lot of reserved mem!)
bffe0000-bffeffff 00010000 Rd NA Reserve Private


With hosting turned off:


...
7ffe1000-7ffeffff 0000f000 NA Free
7fff0000-7fffffff 00010000 NA Reserve Private
80000000-8000ffff 00010000 NA Reserve Private
80010000-bff47fff 3ff38000 NA Free (I like this much better, it gets used by us over time)
bff48000-bff48fff 00001000 RdWr RdWr Commit Private
bff49000-bff49fff 00001000 RdWr RdWr Commit Private
bff4a000-bff4afff 00001000 RdWr RdWr Commit Private
bff4b000-bff4bfff 00001000 RdWr RdWr Commit Private
...