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: <1358412887.2394.0.camel@dabdike.int.hansenpartnership.com>
Date:	Thu, 17 Jan 2013 08:54:47 +0000
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Subhash Jadavani <subhashj@...eaurora.org>,
	martin.petersen@...cle.com, linux-scsi@...r.kernel.org,
	linux-arm-msm@...r.kernel.org, linux-mmc@...r.kernel.org,
	linux-kernel@...r.kernel.org, tj@...nel.org, 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 Wed, 2013-01-16 at 23:14 +0000, Russell King - ARM Linux wrote:
> On Wed, Jan 16, 2013 at 10:32:35AM +0000, James Bottomley wrote:
> > On Wed, 2013-01-16 at 12:07 +0530, Subhash Jadavani wrote:
> > 
> > > Now consider this call stack from MMC block driver (this is on the ARmv7 
> > > based board):
> > >      [   98.918174] [<c001b50c>] (v7_dma_inv_range+0x30/0x48) from 
> > > [<c0017b8c>] (dma_cache_maint_page+0x1c4/0x24c)
> > >      [   98.927819] [<c0017b8c>] (dma_cache_maint_page+0x1c4/0x24c) from 
> > > [<c0017c28>] (___dma_page_cpu_to_dev+0x14/0x1c)
> > >      [   98.937982] [<c0017c28>] (___dma_page_cpu_to_dev+0x14/0x1c) from 
> > > [<c0017ff8>] (dma_map_sg+0x3c/0x114)
> > 
> > OK, so this is showing that ARM itself is making the assumption that the
> > pages are contiguous in the page offset map.
> > 
> > Fix this by doing the increment via the pfn, which will do the right
> > thing whatever the memory model.
> > 
> > Signed-off-by: James Bottomley <JBottomley@...allels.com>
> 
> Ok.  What would you like the patch summary line for this to be -
> the existing one seems to be a little wrong given the content of
> this patch...

how about

arm: fix struct page iterator in dma_cache_maint() to work with
sparsemem

?

James

> > 
> > ---
> > 
> > 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);
> >  		left -= len;
> >  	} while (left);
> >  }
> > 
> > 
> > 
> > _______________________________________________
> > linux-arm-kernel mailing list
> > linux-arm-kernel@...ts.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
> --
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