Re: [PATCH v4 4/7] s390/pci: Use dma-iommu layer

[Niklas Schnelle]

On Thu, 2023-01-19 at 10:59 -0500, Matthew Rosato wrote:
> On 1/19/23 6:03 AM, Niklas Schnelle wrote:
> > > > > > > > > > > > > > > > > >  
> > > > > > > > > > > > > > > > > > 
> > > > > > > > > > > > > > > > > >  static char *pci_sw_names[] = {
> > > > > > > > > > > > > > > > > > - "Allocated pages",
> > > > > > > > > > > > > > > > > > +/* TODO "Allocated pages", */
> > > > > > > > > > 
> > > > > > > > > > ? Forgot to finish this?
> > 
> > Definitely forgot to remove the TODO. I think my latest plan was to
> > just remove this counter. With the DMA API conversion the
> > dma_map_ops.alloc and dma_map_ops.free move to common code and I don't
> > see how we could differentiate these from map/unmap on our side. I'm
> > not sure how helpful this counter really is either. If you're
> > interested in how many pages are mapped long term I think it makes more
> > sense to look at the difference between mapped and unmapped pages. What
> > do you think?
> > > > > > > > > 
> 
> Sounds reasonable to me, but I also note that without this series, when viewing statistics for a device, mapped - unmapped != allocated.  Maybe allocated pages was already broken, or is it taking into account something else that mapped - unmapped would not (maybe mapping the same page multiple times)?
> 
> 

Allocated Pages only counts the memory allocated via dma_map_ops.alloc
so it would not count long term mappings of memory the driver allocated
differently and then mapped for long term use.