SGL support of driver

[Christoph Hellwig]

On Thu, Jul 30, 2015 at 02:38:28PM -0400, Matthew Wilcox wrote:
> I'm not really interested in optimising for badly configured RAID setups :-)
> 
> But point taken, RAID (and other things) can mess with I/Os between the
> page cache and the driver.

With blocksize < pagesize you can also get other non-aligned I/O,
although rately in a way where you could fit multiple of these into a
SGL.