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

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Date:	Wed, 21 May 2014 09:24:50 +0900
From:	Gioh Kim <gioh.kim@....com>
To:	Michal Nazarewicz <mina86@...a86.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>
CC:	Marek Szyprowski <m.szyprowski@...sung.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Heesub Shin <heesub.shin@...sung.com>,
	Mel Gorman <mgorman@...e.de>,
	Johannes Weiner <hannes@...xchg.org>,
	이건호 <gunho.lee@....com>
Subject: Re: [RFC PATCH] arm: dma-mapping: fallback allocation for cma failure



2014-05-21 오전 3:22, Michal Nazarewicz 쓴 글:
> 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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