Re: [PATCH 1/2] dma-mapping: zero memory returned from dma_alloc_*

[Christoph Hellwig]

On Fri, Dec 14, 2018 at 10:54:32AM +0100, Geert Uytterhoeven wrote:
> > -       page = alloc_pages(flag, order);
> > +       page = alloc_pages(flag | GFP_ZERO, order);
> >         if (!page)
> >                 return NULL;
> 
> There's second implementation below, which calls __get_free_pages() and
> does an explicit memset().  As __get_free_pages() calls alloc_pages(), perhaps
> it makes sense to replace the memset() by GFP_ZERO, to increase consistency?

It would, but this patch really tries to be minimally invasive to just
provide the zeroing everywhere.  There is plenty of opportunity
to improve the m68k dma allocator if I can get enough reviewers/testers:

 - for one the coldfire/nommu case absolutely does not make sense to
   me as there is not work done at all to make sure the memory is
   mapped uncached despite the architecture implementing cache
   flushing for the map interface.  So this whole implementation
   looks broken to me and will need some major work (I had a previous
   discussion with Greg on that which needs to be dug out)
 - the "regular" implementation in this patch should probably be replaced
   with the generic remapping helpers that have been added for the 4.21
   merge window:

	http://git.infradead.org/users/hch/dma-mapping.git/commitdiff/0c3b3171ceccb8830c2bb5adff1b4e9b204c1450

Compile tested only patch below:

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