Re: [RFC PATCH] arm: dma-mapping: fallback allocation for cma failure

[Gioh Kim]

2014-05-21 ìì 3:22, Michal Nazarewicz ì ê:
> On Mon, May 19 2014, Joonsoo Kim wrote:
> > On Tue, May 20, 2014 at 02:57:47PM +0900, Gioh Kim wrote:
> > > Thanks for your advise, Michal Nazarewicz.
> > >
> > > Having discuss with Joonsoo, I'm adding fallback allocation after __alloc_from_contiguous().
> > > The fallback allocation works if CMA kernel options is turned on but CMA size is zero.
> >
> > Hello, Gioh.
> >
> > I also mentioned the case where devices have their specific cma_area.
> > It means that this device needs memory with some contraint.
> > Although I'm not familiar with DMA infrastructure, I think that
> > we should handle this case.
> >
> > How about below patch?
> >
> > ------------>8----------------
> > diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
> > index 6b00be1..4023434 100644
> > --- a/arch/arm/mm/dma-mapping.c
> > +++ b/arch/arm/mm/dma-mapping.c
> > @@ -379,7 +379,7 @@ static int __init atomic_pool_init(void)
> >   	unsigned long *bitmap;
> >   	struct page *page;
> >   	struct page **pages;
> > -	void *ptr;
> > +	void *ptr = NULL;
> >   	int bitmap_size = BITS_TO_LONGS(nr_pages) * sizeof(long);
> >
> >   	bitmap = kzalloc(bitmap_size, GFP_KERNEL);
> > @@ -393,7 +393,8 @@ static int __init atomic_pool_init(void)
> >   	if (IS_ENABLED(CONFIG_DMA_CMA))
> >   		ptr = __alloc_from_contiguous(NULL, pool->size, prot, &page,
> >   					      atomic_pool_init);
> > -	else
> > +
> > +	if (!ptr)
> >   		ptr = __alloc_remap_buffer(NULL, pool->size, gfp, prot, &page,
> >   					   atomic_pool_init);
> >   	if (ptr) {
> > @@ -701,10 +702,22 @@ static void *__dma_alloc(struct device *dev, size_t size, dma_addr_t *handle,
> >   		addr = __alloc_simple_buffer(dev, size, gfp, &page);
> >   	else if (!(gfp & __GFP_WAIT))
> >   		addr = __alloc_from_pool(size, &page);
> > -	else if (!IS_ENABLED(CONFIG_DMA_CMA))
> > -		addr = __alloc_remap_buffer(dev, size, gfp, prot, &page, caller);
> > -	else
> > -		addr = __alloc_from_contiguous(dev, size, prot, &page, caller);
> > +	else {
> > +		if (IS_ENABLED(CONFIG_DMA_CMA)) {
> > +			addr = __alloc_from_contiguous(dev, size, prot,
> > +							&page, caller);
> > +			/*
> > +			 * Device specific cma_area means that
> > +			 * this device needs memory with some contraint.
> > +			 * So, we can't fall through general remap allocation.
> > +			 */
> > +			if (!addr && dev && dev->cma_area)
> > +				return NULL;
> > +		}
> > +
> > +		addr = __alloc_remap_buffer(dev, size, gfp, prot,
> > +							&page, caller);
> > +	}
>
> __arm_dma_free will have to be changed to handle the fallback as well.
> But perhaps Marek is right and there should be no fallback for regular
> allocations?  Than again, non-CMA allocation should be performed at
> least in the case of cma=0.


I think in the cases of cma=0, CONFIG_CMA_SIZE_SEL_MBYTES=0 and CONFIG_CMA_SIZE_SEL_PERCENTAGE=0
kernel should be act as like CMA is not turned on.
non-CMA allocation should be performed in the cases.


I will send a patch soon with __arm_dma_free changes.


> >   	if (addr)
> >   		*handle = pfn_to_dma(dev, page_to_pfn(page));
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