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

[Felix Marti]

> -----Original Message-----
> From: general-bounces at lists.openfabrics.org [mailto:general-
> bounces at lists.openfabrics.org] On Behalf Of Roland Dreier
> Sent: Tuesday, February 12, 2008 2:42 PM
> To: Christoph Lameter
> Cc: Rik van Riel; steiner at sgi.com; Andrea Arcangeli;
> a.p.zijlstra at chello.nl; izike at qumranet.com; linux-
> kernel at vger.kernel.org; avi at qumranet.com; linux-mm at kvack.org;
> daniel.blueman at quadrics.com; Robin Holt;
general at lists.openfabrics.org;
> Andrew Morton; kvm-devel at lists.sourceforge.net
> Subject: Re: [ofa-general] Re: Demand paging for memory regions
> 
>  > > Chelsio's T3 HW doesn't support this.
> 
>  > Not so far I guess but it could be equipped with these features
> right?
> 
> I don't know anything about the T3 internals, but it's not clear that
> you could do this without a new chip design in general.  Lot's of RDMA
> devices were designed expecting that when a packet arrives, the HW can
> look up the bus address for a given memory region/offset and place the
> packet immediately.  It seems like a major change to be able to
> generate a "page fault" interrupt when a page isn't present, or even
> just wait to scatter some data until the host finishes updating page
> tables when the HW needs the translation.

That is correct, not a change we can make for T3. We could, in theory,
deal with changing mappings though. The change would need to be
synchronized though: the VM would need to tell us which mapping were
about to change and the driver would then need to disable DMA to/from
it, do the change and resume DMA.

> 
>  - R.
> 
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