linux-kernel - Re: swiotlb detection should be memory hotplug aware ?

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Message-Id: <20100722084413I.fujita.tomonori@lab.ntt.co.jp>
Date:	Thu, 22 Jul 2010 08:44:42 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	akataria@...are.com
Cc:	fujita.tomonori@....ntt.co.jp, konrad.wilk@...cle.com,
	ak@...ux.intel.com, lenb@...nel.org, x86@...nel.org,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
	petr@...are.com
Subject: Re: swiotlb detection should be memory hotplug aware ?

On Wed, 21 Jul 2010 10:13:34 -0700
Alok Kataria <akataria@...are.com> wrote:

> > Basically, you want to add hot-plug memory and enable swiotlb, right?
> 
> Not really, I am planning to do something like this, 
> 
> @@ -52,7 +52,7 @@ int __init pci_swiotlb_detect(void)
>  
>  	/* don't initialize swiotlb if iommu=off (no_iommu=1) */
>  #ifdef CONFIG_X86_64
> -	if (!no_iommu && max_pfn > MAX_DMA32_PFN)
> +	if (!no_iommu && (max_pfn > MAX_DMA32_PFN || hotplug_possible()))
>  		swiotlb = 1;

Always enable swiotlb with memory hotplug enabled? Wasting 64MB on a
x86_64 system with 128MB doesn't look to be a good idea. I don't think
that there is an easy solution for this issue though.
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