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Message-Id: <1158955850.24572.37.camel@localhost.localdomain>
Date: Fri, 22 Sep 2006 21:10:50 +0100
From: Alan Cox <alan@...rguk.ukuu.org.uk>
To: Andi Kleen <ak@...e.de>
Cc: Christoph Lameter <clameter@....com>,
Martin Bligh <mbligh@...igh.org>, akpm@...gle.com,
linux-kernel@...r.kernel.org,
Christoph Hellwig <hch@...radead.org>,
James Bottomley <James.Bottomley@...eleye.com>,
linux-mm@...ck.org
Subject: Re: [RFC] Initial alpha-0 for new page allocator API
Ar Gwe, 2006-09-22 am 21:10 +0200, ysgrifennodd Andi Kleen:
> We already have that scheme. Any existing driver should be already converted
> away from GFP_DMA towards dma_*/pci_*. dma_* knows all the magic
> how to get memory for the various ranges. No need to mess up the
> main allocator.
Add an isa_device class and that'll fall into place nicely. isa_alloc_*
will end up asking for 20bit DMA and it will work nicely.
> Anyways, i suppose what could be added as a fallback would be a
> really_slow_brute_force_try_to_get_something_in_this_range() allocator
Implementation detail although I note that the defrag/antifrag proposal
made at the vm summit would mean it mostly come out for free. If we have
an isa_dma_* API then the detail is platform specific.
> that basically goes through the buddy lists freeing in >O(1)
> and does some directed reclaim, but that would likely be a separate
> path anyways and not need your new structure to impact the O(1)
> allocator.
Just search within the candidate 4MB (or whatever it is these days)
chunks.
> I am still unconvinced of the real need. The only gaping hole was
> GFP_DMA32, which we fixed already.
Various devices are 30 and 31bit today - some broadcom for example.
> Ok there is aacraid with its weird 2GB limit,
> Ok now I'm sure someone will come up with a counter example (hi Alan), but:
> - Does the device really need more than 16MB?
> - How often is it used on systems with >1/2GB with a 64bit kernel?
> [consider that 64bit kernels don't support ISA]
> - How many users of that particular thing around?
Ok the examples I know about are
- ESS Maestro series audio - PCI, common on 32bit boxes a few years ago,
no longer shipped and unlikely to be met on 64bit. Also slow allocations
is fine.
- Some aacraid, mostly only for control structures. Those found on 64bit
are probably fine with slow alloc.
- Broadcom stuff - not sure if 30 or 31bit, around today and on 64bit
- Floppy controller
> I think my point stands.
I think its worthy of discussion.
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