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

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Message-ID: <20130117103742.GX23505@n2100.arm.linux.org.uk>
Date:	Thu, 17 Jan 2013 10:37:42 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	James Bottomley <James.Bottomley@...senPartnership.com>
Cc:	Tejun Heo <tj@...nel.org>,
	Subhash Jadavani <subhashj@...eaurora.org>,
	linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
	linux-mmc@...r.kernel.org, linux-arm-msm@...r.kernel.org,
	martin.petersen@...cle.com, asias@...hat.com,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 1/1] block: blk-merge: don't merge the pages with
	non-contiguous descriptors

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?
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