Re: [PATCH 1/3] direct-io: add a hook for the fs to provide its own bio merging check function

[Chris Mason <chris.mason@oracle.com>]

Excerpts from Miao Xie's message of 2010-11-17 20:18:18 -0500:
> >> Right thats the idea, if we can't span chunks/stripes we should be doing that
> >> limiting in our get_blocks call and that way we don't have to screw with the
> >> generic direct io stuff too much.  Thanks,
> >
> > In this case we're adding complexity to the O_DIRECT mapping code, when
> > we really should be adding it to the btrfs submit bio hook.  It can
> > easily break up the bio into smaller units, which will leave us with a
> > smaller number of get_blocks calls overall.
> >
> > I'm working that out now.
> 
> Do you mean you are fixing this bug now?

I started on it this afternoon, but lost network due to high winds here.
So, I didn't make any real progress.

If you'd like to fix this in the btrfs direct-io bio submit call you're
welcome to continue working on it.

The idea is to just clone and split up the bio, which will keep us from
filling up fs/direct-io.c w/btrfs rules and allow us to take fewer
trips into the get_blocks call.

-chris