[openib-general] [PATCH] kDAPL: cleanup dat/ a bit more

[David Addison]

Caitlin Bestler wrote:
> On 6/4/05, Christoph Hellwig <hch at lst.de> wrote:
> 

> The Quadrics patch informed zero copy devices
> of new mappings, but does so when the device
> is not actively doing work. That latter piece of
> information is not available for an RDMA device.
> For normal devices the OS has a reasonable
> expectation on when the device is performing
> DMA, because it is doing so in response to a
> request that the OS knows about. For an RDMA
> device a DMA transfer can be in progress as
> as a result of an RDMA Read -- something the
> host processor knows nothing about.

The Quadrics devices can handle changes in page mappings
whilst RDMA operations are in progress. If say a page
is being evicted due to swap pressure, then the Quadrics
NIC is first informed by an IOPROC invalidate call. This
will cause any future device accesses to that page to
fault and the network operation to stall.
The Quadrics NIC will continue the RDMA once a new valid
translation has been loaded by the OS.


Cheers
Addy.