[linux-lvm] Re: dm, dm_table, request_queue

[Miquel van Smoorenburg]

On Tue, 24 Feb 2004 10:03:56, Joe Thornber wrote:
> On Tue, Feb 24, 2004 at 01:21:16AM +0100, Miquel van Smoorenburg wrote:
> > All in all, I think that the first approach is the simplest and
> > therefor the best.
> > 
> > So how does this look:
> 
> Better wrt keeping mapped_device out of dm-table.c.  But it still has
> the problem that it treats congestion in any subdevices equally (which
> may be a good approximation to start with).

The only other solution I see is to 1) add a mechanism for non-blocking
generic_make_request() calls (returning EAGAIN) and 2) a way to check
for congestion of a block device with (offset, len) parameters.

It's hard though. You'd need request reservations on a queue that you
can cancel later on if you discover that the whole multi-device request
cannot be made. Something like a transaction with multiple requests.

But that's currently a bit over my head at least and not 2.6 material
either I think.

Mike.