I own a 2013 Mazda 6 diesel and have the same issues with the dpf as others have described in CarsGuide. Mazda has failed us all in terms of addressing this issue and have basically fobbed us off each time, denying there is a major problem.
We understand Mazda released a revised engine oil dipstick with a higher full mark. It also released revised software for the dpf operation that changed the way the self-cleaning function took place. If you haven’t got those updates I would be approaching Mazda to get your car updated.