linux-kernel - Re: ZONE

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Date:	Fri, 22 Sep 2006 10:39:28 -0700
From:	Jesse Barnes <jesse.barnes@...el.com>
To:	Christoph Lameter <clameter@....com>
Cc:	Martin Bligh <mbligh@...igh.org>, Andrew Morton <akpm@...l.org>,
	linux-kernel@...r.kernel.org, Rohit Seth <rohitseth@...gle.com>
Subject: Re: ZONE_DMA

On Friday, September 22, 2006 10:21 am, Jesse Barnes wrote:
> If you have a decent enough IOMMU both or either could cover all of
> memory. In the case of an Altix, the IOMMU is 32 bit capable, so it
> would make sense for ZONE_DMA32 to contain all of memory...
>
> But anyway, I agree with your broader point that we really need a
> different allocator for this stuff.  It has to be arch specific in some
> way though, so we can take into account the advantages IOMMUs provide. 
> I think jejb said he'd come up with a sample implementation a couple of
> years ago... :)
>
> From a portability and definition perspective, I'd contend that ZONE_DMA
> and ZONE_DMA32 are both broken.  Only ZONE_NORMAL and ZONE_HIGHMEM have
> sane definitions it seems.

Ok and right after I sent this my brain returned from vacation and I 
remembered jejb's DMA allocation API.  It's powerful enough to cover most 
driver use cases I think (users of GFP_DMA should probably be converted), 
but for example block layer bounce buffering might need a different 
interface as I see you've proposed in another mail.

Hm... s390 driver seem to like GFP_DMA a lot...  and there are a few 
remaining uses in drivers/scsi... and then of course there are the OSS 
drivers...

Jesse
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