Maximum NVMe IO command size > 1MB?

[Xuehua Chen]

Hi, 

It seems to me kernel 4.3 supports NVMe IO command size > 512k after the following is added. 

blk_queue_max_segments(ns->queue,
       ((dev->max_hw_sectors << 9) / dev->page_size) + 1);

If I run the fllowing, 
fio --name=iotest --filename=/dev/nvme0n1 --iodepth=1 --ioengine=libaio --direct=1 --size=1M --bs=1M --rw=read

I can see one read with data transfer size 1MB is sent to device. 

But if I increase the bs to 2M as below, I still see two 1MB commands are sent out instead of one 2MB read command
fio --name=iotest --filename=/dev/nvme0n1 --iodepth=1 --ioengine=libaio --direct=1 --size=2M --bs=2M --rw=read

Is there any other settings in kernel that make it split a 2M command into two 1M commands? 

Thanks, 

Xuehua