Subject: ask for help about swiotlb buffer is full

From: [email-masked] (Kefeng Wang)
Date: Wed, 4 Feb 2015 20:01:01 +0800

On 2015-02-03 2:24, Catalin Marinas wrote:
> On Sat, Jan 31, 2015 at 04:00:06AM +0000, Kefeng Wang wrote:
>> On 2015-01-30 19:59, Catalin Marinas wrote:
[...]
>>>
>>
>> 4kb page,  use Make ARCH=arm64 defconfig in v3.19 to generate config.
>>
>> [    0.678293] software IO TLB [mem 0x7e800000-0x7ec00000] (4MB) mapped at [ffffffc07e800000-ffffffc07ebfffff]
>> [    0.686991] DMA: preallocated 256 KiB pool for atomic allocations
> 
> Was the swiotlb buffer size the same in the 3.16 kernel? The only thing
> I recall adding was the atomic pool allocations but these are only for
> non-coherent DMA ops and only for dma_alloc/free. I assume, in the case
> of SATA, the failure is on the dma_map_sg() path.

Swiotlb buffer size is both 4M in v3.16 and v3.19-rc4, and the failure is
on the dma_map_sg() -> swiotlb_map_sg_attrs.

> 
> Maybe with a 3.19 kernel you get more than 4MB swiotlb buffers used at a
> time with your tests; can you try increasing this via a kernel command
> like to, let's say, 8MB? If I got my calculations correctly (an IO TLB
> slab is 1 << 11):
> 
> 	swiotlb=4096
> 
> If it still runs out with bigger buffers, we may need to look into
> potential leaks.
> 

The buddy allocator can only support 4M contiguous physical memory, so it's
useless to increase swiotlb buffer.