On Sun, Oct 26, 2014 at 12:02 PM, Mayuresh Kathe <mayur...@devio.us> wrote:
> 64-bit supposedly supports upto 16 exabytes of memory ('ram').
> would such large capacities actually be possible to ue with
> openbsd for amd64 architecture?
> use-case: working with large in-memory storage for financial applications.Currently, in the amd64 pmap we only allocate a single PML4 slot for the 'direct' map, limiting the system to 512GB of physical memory. Multiplying that by a factor of 4 or even 64 would be easy, but lacking someone actually planning to *use and test* that it just hasn't been seen as worth the effort to do, verify the change in kva layout doesn't break some hidden assumption, etc. (IIRC, dlg@ did this once just to get a dmesg from a 2TB machine going to other, non-OpenBSD use.) There's an upper limit to that growth: there's only 256 PML4 slots for kva, from which this comes, so at some point the kva remaining for normal use and management would shrink too much and the whole pmap would need to be rethought... Philip Guenther
