Re: [PATCH for-dm-3.14-fixes 2/8] dm thin: set flag when over the metadata low watermark threshold

[Mike Snitzer <snitzer@redhat.com>]

On Fri, Feb 21 2014 at  9:05am -0500,
Mike Snitzer <snitzer@redhat.com> wrote:

> On Fri, Feb 21 2014 at  8:56am -0500,
> Joe Thornber <thornber@redhat.com> wrote:
> 
> > NACK
> 
> You can NACK all you want.  Old code doesn't work.  New code does.
> 
> > On Thu, Feb 20, 2014 at 09:55:59PM -0500, Mike Snitzer wrote:
> > > The threshold boundary code in persistent-data/dm-space-map-metadata.c
> > > was too racey and resulted in a flood of warnings and events.
> > 
> > This code never runs concurrently, so I don't see how it can be racey.
> > Scanning the code it seems to work as advertised; it is an edge
> > triggered threshold, activating every time the free space crosses the
> > threshold from high to low.
> > 
> > - You haven't explained what your changes within
> >   dm-space-map-metadata.c do.  Is the threshold no longer edge
> >   triggered?
> 
> It is identical to data device's low water mark.

To be clear, it is still edge triggered from the metadata sm -- it makes
the same upcall to t->fn(t->context).

Only difference dm-thin.c:metadata_low_callback controls the throttle on
the event and warning.