Host Memory Buffer as DRAM

[QiDeng]

I use HMB as DRAM to store data for FPGA processing later. The hardware is sbRIO-9637. 

I write a simple code to write the data into the DRAM on FPGA and read it back from FPGA. There is no issue if the data points are 256, 512, 1024. But if the data points are not these numbers such as 250, 500, 1000. The read back value are not what I sent. What am I going to do if I want the data points are 250, 500, 1000?

The attachment is the code.