linux-kernel - Re: [PATCH 30/67] dma-direct: retry allocations using GFP

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Date:   Tue, 2 Jan 2018 16:43:15 +0000
From:   Vladimir Murzin <vladimir.murzin@....com>
To:     Christoph Hellwig <hch@....de>, iommu@...ts.linux-foundation.org
Cc:     linux-mips@...ux-mips.org, linux-ia64@...r.kernel.org,
        linux-sh@...r.kernel.org, sparclinux@...r.kernel.org,
        Guan Xuetao <gxt@...c.pku.edu.cn>, linux-arch@...r.kernel.org,
        linux-s390@...r.kernel.org, linux-c6x-dev@...ux-c6x.org,
        linux-hexagon@...r.kernel.org, x86@...nel.org,
        linux-snps-arc@...ts.infradead.org,
        adi-buildroot-devel@...ts.sourceforge.net,
        linux-m68k@...ts.linux-m68k.org, patches@...ups.riscv.org,
        linux-metag@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Michal Simek <monstr@...str.eu>, linux-parisc@...r.kernel.org,
        linux-cris-kernel@...s.com, linux-kernel@...r.kernel.org,
        linux-alpha@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 30/67] dma-direct: retry allocations using GFP_DMA for
 small masks

On 29/12/17 08:18, Christoph Hellwig wrote:
> If we got back an allocation that wasn't inside the support coherent mask,
> retry the allocation using GFP_DMA.
> 
> Based on the x86 code.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>  lib/dma-direct.c | 25 ++++++++++++++++++++++++-
>  1 file changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/dma-direct.c b/lib/dma-direct.c
> index ab81de3ac1d3..f8467cb3d89a 100644
> --- a/lib/dma-direct.c
> +++ b/lib/dma-direct.c
> @@ -28,6 +28,11 @@ check_addr(struct device *dev, dma_addr_t dma_addr, size_t size,
>  	return true;
>  }
>  
> +static bool dma_coherent_ok(struct device *dev, phys_addr_t phys, size_t size)
> +{
> +	return phys_to_dma(dev, phys) + size <= dev->coherent_dma_mask;

Shouldn't it be: phys_to_dma(dev, phys) + size - 1 <= dev->coherent_dma_mask ?

> +}
> +
>  static void *dma_direct_alloc(struct device *dev, size_t size,
>  		dma_addr_t *dma_handle, gfp_t gfp, unsigned long attrs)
>  {
> @@ -35,11 +40,29 @@ static void *dma_direct_alloc(struct device *dev, size_t size,
>  	int page_order = get_order(size);
>  	struct page *page = NULL;
>  
> +again:
>  	/* CMA can be used only in the context which permits sleeping */
> -	if (gfpflags_allow_blocking(gfp))
> +	if (gfpflags_allow_blocking(gfp)) {
>  		page = dma_alloc_from_contiguous(dev, count, page_order, gfp);
> +		if (page && !dma_coherent_ok(dev, page_to_phys(page), size)) {
> +			dma_release_from_contiguous(dev, page, count);
> +			page = NULL;
> +		}
> +	}
>  	if (!page)
>  		page = alloc_pages_node(dev_to_node(dev), gfp, page_order);
> +
> +	if (page && !dma_coherent_ok(dev, page_to_phys(page), size)) {
> +		__free_pages(page, page_order);
> +		page = NULL;
> +
> +		if (dev->coherent_dma_mask < DMA_BIT_MASK(32) &&
> +		    !(gfp & GFP_DMA)) {
> +			gfp = (gfp & ~GFP_DMA32) | GFP_DMA;
> +			goto again;

Shouldn't we limit number of attempts?

Thanks
Vladimir