We can fail seting up Xen-SWIOTLB if:
- The host does not have enough contiguous DMA32 memory available
(can happen on a machine that has fragmented memory from starting,
stopping many guests).
- Not enough low memory (almost never happens).
We retry allocating and exchanging the swath of contiguous memory
up to three times. Each time we decrease the amount we need - the
minimum being of 2MB.
If we compleltly fail, we will print the reason for failure on the Xen
console on top of doing it to earlyprintk=xen console.
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
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