linux-kernel - Re: [PATCH 5/6] swiotlb: Make swiotlb bookkeeping functions visible in the header file.

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Date:	Wed, 19 May 2010 08:10:57 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
Cc:	albert_herranz@...oo.es, konrad.wilk@...cle.com,
	Ian.Campbell@...citrix.com, jeremy@...p.org,
	linux-kernel@...r.kernel.org, chrisw@...s-sol.org,
	iommu@...ts.linux-foundation.org, dwmw2@...radead.org
Subject: Re: [PATCH 5/6] swiotlb: Make swiotlb bookkeeping functions
	visible in the header file.

On Wed, May 19, 2010 at 12:34:18PM +0900, FUJITA Tomonori wrote:
> On Tue, 18 May 2010 18:52:17 +0200
> Albert Herranz <albert_herranz@...oo.es> wrote:
> > Every single KB counts on the Wii. It has just 24MB of MEM1 and 64MB of MEM2 (discontiguous memory ranges).
> > I'm using 1MB for the SWIOTLB for now, but of course that can be further tweaked down.
> 
> You can decrease the swiotlb memory however you can't fix the root
> problems of swiotlb:
> 
> - it needs pre-allocated memory
> - it can't handle the out-of-pre-allocated memory situation.

That's actually the advantage of swiotlb over dmabounce.  dmabounce's
dynamic allocation results in OOMs under some IO activity patterns.
dmabounce also produces the occasional WARN_ON() from the dma coherent
allocator depending on the driver.

We really need to kill off dmabounce.
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