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

From: [email-masked] (Sergei Shtylyov)
Date: Thu, 20 Jun 2013 17:04:32 +0400

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 <[email-masked]>
> ---
>   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 ()?

WBR, Sergei