Re: Is __dma_direct_alloc_pages broken on s390?

[Halil Pasic <pasic@linux.ibm.com>]

On Thu, 18 Jul 2019 06:10:59 -0700
Christoph Hellwig <hch@infradead.org> wrote:

> On Thu, Jul 18, 2019 at 02:50:44PM +0200, Halil Pasic wrote:
> > > I wondered why the kernel works OK on my system, and it is in fact not
> > > so bad. If the first allocation fails, the kernel adds GFP_DMA and
> > > retries, so this is not fatal, but with a proper definition of
> > > ARCH_ZONE_DMA_BITS it should be possible to get success in the first
> > > attempt already, let's do it.
> > > 
> > > Petr T
> > 
> > I fully agree! I will post a patch that provides correct
> > ARCH_ZONE_DMA_BITS for s390.
> > 
> > BTW I wonder if ARCH_ZONE_DMA_BITS can be inferred from MAX_DMA_ADDRESS,
> > and why do we need both.@Christoph, maybe you can help me understand if
> > there is a relationship between the two or not, or?
> 
> MAX_DMA_ADDRESS is a bit of a weird beast which I honestly do not
> understand fully, but most of the uses in common code look a little
> bogus, and we should probably get rid of it.

Thanks!

Regards,
Halil