Messages in this thread | | | Date | Wed, 23 Jan 2008 13:04:46 +0100 | From | Andrea Arcangeli <> | Subject | Re: [kvm-devel] [PATCH] export notifier #1 |
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On Wed, Jan 23, 2008 at 04:52:47AM -0600, Robin Holt wrote: > But 100 callouts holding spinlocks will not work for our implementation > and even if the callouts are made with spinlocks released, we would very > strongly prefer a single callout which messages the range to the other > side.
But you take the physical address and turn into mm+va with your rmap...
> > Also, our rmap key for finding the spte is keyed on (mm, va). I imagine > > most RDMA cards are similar. > > For our RDMA rmap, it is based upon physical address.
so why do you turn it into mm+va?
> >> There is only the need to walk twice for pages that are marked Exported. > >> And the double walk is only necessary if the exporter does not have its > >> own rmap. The cross partition thing that we are doing has such an rmap and > >> its a matter of walking the exporters rmap to clear out the external > >> references and then we walk the local rmaps. All once. > >> > > > > The problem is that external mmus need a reverse mapping structure to > > locate their ptes. We can't expand struct page so we need to base it on mm > > + va. > > Our rmap takes a physical address and turns it into mm+va.
Why don't you stick to mm+va and use get_user_pages and let the VM do the swapins etc...?
> > Can they wait on that bit? > > PageLocked(page) should work, right? We already have a backoff > mechanism so we expect to be able to adapt it to include a > PageLocked(page) check.
It's not PageLocked but wait_on_page___not___exported() called on the master node. Plus nothing in the VM of the master node calls SetPageExported... good luck to make it work (KVM swapping OTOH works like a charm already w/o the backwards secondary-TLB-flushing order).
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