[PATCH] ARM: dma: Drop __GFP_COMP for iommu dma memory allocations

[Richard Zhao]

On Fri, Jun 21, 2013 at 5:33 PM, Marek Szyprowski
<m.szyprowski at samsung.com> wrote:> Hello,
>
>
> On 6/20/2013 3:04 PM, Sergei Shtylyov wrote:
>>
>> Hello.
>>
>> On 20-06-2013 16:31, Richard Zhao wrote:
>>
>>> __iommu_alloc_buffer wants to split pages after allocation in order to
>>> reduce the memory footprint. This does not work well with __GFP_COMP
>>> pages, so drop this flag before allocation
>>
>>
>>> One failure example is snd_malloc_dev_pages call dma_alloc_coherent with
>>> __GFP_COMP.
>>
>>
>>> Signed-off-by: Richard Zhao <rizhao at nvidia.com>
>>> ---
>>>   arch/arm/mm/dma-mapping.c |    9 +++++++++
>>>   1 file changed, 9 insertions(+)
>>
>>
>>> diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
>>> index ef3e0f3..f7efffd 100644
>>> --- a/arch/arm/mm/dma-mapping.c
>>> +++ b/arch/arm/mm/dma-mapping.c
>>> @@ -1314,6 +1314,15 @@ static void *arm_iommu_alloc_attrs(struct device
>>> *dev, size_t size,
>>>       if (gfp & GFP_ATOMIC)
>>>           return __iommu_alloc_atomic(dev, size, handle);
>>>
>>> +    /*
>>> +     * Following is a work-around (a.k.a. hack) to prevent pages
>>> +     * with __GFP_COMP being passed to split_page() which cannot
>>> +     * handle them.  The real problem is that this flag probably
>>> +     * should be 0 on ARM as it is not supported on this
>>> +     * platform; see CONFIG_HUGETLBFS.
>>> +     */
>>> +    gfp &= ~(__GFP_COMP);
>>
>>
>>    Hm, what exactly is the sense you meant in using ()?
>
>
> I think that those parentheses come from the first patch, which disabled
> __GFP_COMP
> in dma-mapping allocations: 3611553ef98 ("[AVR32] Drop GFP_COMP for DMA
> memory
> allocations"). I would like to take this patch to the dma-mapping tree
> together with
> other changes related to iommu integration code.
Thanks! I'm not sure. Do we still have time to have this fix on 3.10?

Richard
>
> Best regards
> --
> Marek Szyprowski
> Samsung R&D Institute Poland
>
>
>
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel at lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel