[PATCH v2 1/1] block: blk-merge: don't merge the pages with non-contiguous descriptors

[Russell King - ARM Linux]

On Thu, Jan 17, 2013 at 09:11:20AM +0000, James Bottomley wrote:
> On Wed, 2013-01-16 at 15:18 -0800, Tejun Heo wrote:
> > On Wed, Jan 16, 2013 at 10:32:35AM +0000, James Bottomley wrote:
> > > diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
> > > index 6b2fb87..ab88c5b 100644
> > > --- a/arch/arm/mm/dma-mapping.c
> > > +++ b/arch/arm/mm/dma-mapping.c
> > > @@ -809,7 +809,7 @@ static void dma_cache_maint_page(struct page *page, unsigned long offset,
> > >  			op(vaddr, len, dir);
> > >  		}
> > >  		offset = 0;
> > > -		page++;
> > > +		page = pfn_to_page(page_to_pfn(page) + 1);
> > 
> > Probably page = nth_page(page, 1) is the better form.
> 
> It's the same thing.
> 
> I'd actually prefer page = pfn_to_page(page_to_pfn(page) + 1); because
> it makes the code look like the hack it is.  The preferred form for all
> iterators like this should be to iterate over the pfn instead of a
> pointer into the page arrays, because that will always work correctly no
> matter how many weird and wonderful memory schemes we come up with.

So, why don't we update the code to do that then?