On 14 Jul 1999, Chris G. Demetriou wrote: > Doug Rabson <d...@nlsystems.com> writes: > > Overcommit can be used for many reasons. I use it to reserve a large > > linear address space to mmap alpha i/o spaces [...] > > Overcommit can be used for many reasons, but unless you've > misdescribed what you're doing, _that's not one of them_. > > The mapped I/O pages need no backing store to be allocated for them by > the VM system. They're backed by hardware. > > And if you have 'placeholder' pages (I note that you didn't say you > mmap all of alpha i/o space, just reserve a large linear address space > in which to mmap it), then it should be possible to map them in such a > way (e.g. read-only ZFOD) in which they wouldn't count against backing > store requirements, either.
I certainly don't need or want backing store for these pages. The original reserved region is never touched without first mapping device pages onto it. -- Doug Rabson Mail: d...@nlsystems.com Nonlinear Systems Ltd. Phone: +44 181 442 9037 To Unsubscribe: send mail to majord...@freebsd.org with "unsubscribe freebsd-hackers" in the body of the message
