linux-kernel - Re: [PATCH 1/3] swiotlb: Warn on allocation failure in swiotlb_alloc

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Date:	Mon, 1 Dec 2014 15:28:03 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Joerg Roedel <joro@...tes.org>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org, Joerg Roedel <jroedel@...e.de>
Subject: Re: [PATCH 1/3] swiotlb: Warn on allocation failure in
 swiotlb_alloc_coherent

On Fri, Nov 28, 2014 at 12:29:07PM +0100, Joerg Roedel wrote:
> From: Joerg Roedel <jroedel@...e.de>
> 
> Print a warning when all allocation tries have been failed
> and the function is about to return NULL. This prepares for
> calling the function with __GFP_NOWARN to suppress
> allocation failure warnings before all fall-backs have
> failed.

This can be quite noisy. Especially the dump-stack.

Perhaps have this trigger is the 'verbose' or 'debug' (new) parameter
would be added to the 'swiotlb' one?

> 
> Signed-off-by: Joerg Roedel <jroedel@...e.de>
> ---
>  lib/swiotlb.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/swiotlb.c b/lib/swiotlb.c
> index 4abda07..e0e9212 100644
> --- a/lib/swiotlb.c
> +++ b/lib/swiotlb.c
> @@ -655,7 +655,7 @@ swiotlb_alloc_coherent(struct device *hwdev, size_t size,
>  		 */
>  		phys_addr_t paddr = map_single(hwdev, 0, size, DMA_FROM_DEVICE);
>  		if (paddr == SWIOTLB_MAP_ERROR)
> -			return NULL;
> +			goto err_warn;
>  
>  		ret = phys_to_virt(paddr);
>  		dev_addr = phys_to_dma(hwdev, paddr);
> @@ -669,7 +669,7 @@ swiotlb_alloc_coherent(struct device *hwdev, size_t size,
>  			/* DMA_TO_DEVICE to avoid memcpy in unmap_single */
>  			swiotlb_tbl_unmap_single(hwdev, paddr,
>  						 size, DMA_TO_DEVICE);
> -			return NULL;
> +			goto err_warn;
>  		}
>  	}
>  
> @@ -677,6 +677,13 @@ swiotlb_alloc_coherent(struct device *hwdev, size_t size,
>  	memset(ret, 0, size);
>  
>  	return ret;
> +
> +err_warn:
> +	pr_warn("swiotlb: coherent allocation failed for device %s size=%zu\n",
> +		dev_name(hwdev), size);
> +	dump_stack();
> +
> +	return NULL;
>  }
>  EXPORT_SYMBOL(swiotlb_alloc_coherent);
>  
> -- 
> 1.9.1
> 
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