clSVMAlloc() failure on i5 6500

Hi

We are trying to use Opencl with i5 6500.When we use clSVMAlloc() for SVM over a certain size,it will return failure.The questions as belows:

1. What factor decides the max SVM size ?(The size of host memory ? );

2.How does SVM work on physical storage?

3.How can I get the value of max SVM size on my platform?

regards.