[ofa-general] Re: Demand paging for memory regions

[Christoph Lameter]

On Fri, 15 Feb 2008, Caitlin Bestler wrote:

> > What does it mean that the "application layer has to be determine what
> > pages are registered"? The application does not know which of its
> pages
> > are currently in memory. It can only force these pages to stay in
> > memory if their are mlocked.
> > 
> 
> An application that advertises an RDMA accessible buffer
> to a remote peer *does* have to know that its pages *are*
> currently in memory.

Ok that would mean it needs to inform the VM of that issue by mlocking 
these pages.
 
> But the more fundamental issue is recognizing that applications
> that use direct interfaces need to know that buffers that they
> enable truly have committed resources. They need a way to
> ask for twenty *real* pages, not twenty pages of address
> space. And they need to do it in a way that allows memory
> to be rearranged or even migrated with them to a new host.

mlock will force the pages to stay in memory without requiring the OS to 
keep them where they are.