Maximum NVMe IO command size > 1MB?

[Keith Busch]

On Wed, Jan 06, 2016 at 09:56:24PM +0000, Xuehua Chen wrote:
> Hi, Keith, 
> 
> I wonder whether this could be caused by BIO_MAX_PAGES defined as 256, which means 1MB at most.
> What do you think?

I think you got it. You're running O_DIRECT, and fs/direct-io.c,
dio_new_bio() allocates up to BIO_MAX_PAGES.

I can't tell where the value for came from (looks like it was there from
the very first git commit), but maybe you can propose raising it if you
set BIO_MAX_PAGES higher without issue.