Messages in this thread | | | Date | Wed, 10 Jun 2015 09:00:31 -0700 | Subject | Re: [PATCH 1/2] scatterlist: use sg_phys() | From | Dan Williams <> |
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On Wed, Jun 10, 2015 at 2:32 AM, Joerg Roedel <joro@8bytes.org> wrote: > On Tue, Jun 09, 2015 at 12:27:10PM -0400, Dan Williams wrote: >> diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c >> index 7e7583ddd607..9f6ff6671f01 100644 >> --- a/arch/arm/mm/dma-mapping.c >> +++ b/arch/arm/mm/dma-mapping.c >> @@ -1502,7 +1502,7 @@ static int __map_sg_chunk(struct device *dev, struct scatterlist *sg, >> return -ENOMEM; >> >> for (count = 0, s = sg; count < (size >> PAGE_SHIFT); s = sg_next(s)) { >> - phys_addr_t phys = page_to_phys(sg_page(s)); >> + phys_addr_t phys = sg_phys(s) - s->offset; > > So sg_phys() turns out to be 'page_to_phys(sg_page(s)) + s->offset', > which makes the above statement to: > > page_to_phys(sg_page(s)) + s->offset - s->offset; > > The compiler will probably optimize that away, but it still doesn't look > like an improvement.
The goal is to eventually stop leaking struct page deep into the i/o stack. Anything that relies on being able to retrieve a struct page out of an sg entry needs to be converted. I think we need a new helper for this case "sg_phys_aligned()?".
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