linux-kernel - Re: [PATCH] swiotlb: suppress warning when __GFP

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Date:   Thu, 4 Jan 2018 11:16:39 +0100
From:   Christian König <ckoenig.leichtzumerken@...il.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     konrad.wilk@...cle.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] swiotlb: suppress warning when __GFP_NOWARN is set v4

Am 04.01.2018 um 10:53 schrieb Christoph Hellwig:
> This seems to collide with my dma direct/swiotlb series posted recently.
>
>> +++ b/lib/swiotlb.c
>> @@ -490,11 +490,11 @@ static void swiotlb_bounce(phys_addr_t orig_addr, phys_addr_t tlb_addr,
>>   	}
>>   }
>>   
>> -phys_addr_t swiotlb_tbl_map_single(struct device *hwdev,
>> -				   dma_addr_t tbl_dma_addr,
>> -				   phys_addr_t orig_addr, size_t size,
>> -				   enum dma_data_direction dir,
>> -				   unsigned long attrs)
>> +static phys_addr_t tbl_map_single(struct device *hwdev,
>> +				  dma_addr_t tbl_dma_addr,
>> +				  phys_addr_t orig_addr, size_t size,
>> +				  enum dma_data_direction dir,
>> +				  unsigned long attrs, bool warn)
> We already have DMA_ATTR_NO_WARN which can be passed in attrs.  Please
> use it instead of reinventing it.
>
>>   swiotlb_alloc_coherent(struct device *hwdev, size_t size,
>>   		       dma_addr_t *dma_handle, gfp_t flags)
>>   {
>> +	bool warn = !(flags & __GFP_NOWARN);
>>   	dma_addr_t dev_addr;
>>   	void *ret;
>>   	int order = get_order(size);
>> @@ -739,7 +750,7 @@ swiotlb_alloc_coherent(struct device *hwdev, size_t size,
>>   		 * will grab memory from the lowest available address range.
>>   		 */
>>   		phys_addr_t paddr = map_single(hwdev, 0, size,
>> -					       DMA_FROM_DEVICE, 0);
>> +					       DMA_FROM_DEVICE, 0, warn);
> Note: in my above series swiotlb_alloc_coherent is going away, and
> replaced with a swiotlb_alloc that takes a dma_attrs argument.

That's what I thought about as well, but this is a bug fix for stable 
kernels. So the changes should be as small as possible.

But using DMA_ATTR_NO_WARN is a good point, going to send a v5 which 
uses this instead.

Regards,
Christian.

>
> Using that for passing the nowarn flag is the right way to go instead
> of using __GFP_NOWARN.