linux-kernel - Re: [Intel-IOMMU 02/10] Library routine for pre-allocat pool handling

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Date:	Mon, 11 Jun 2007 14:14:49 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Keshavamurthy, Anil S" <anil.s.keshavamurthy@...el.com>
Cc:	Andi Kleen <ak@...e.de>, Christoph Lameter <clameter@....com>,
	linux-kernel@...r.kernel.org, gregkh@...e.de, muli@...ibm.com,
	asit.k.mallick@...el.com, suresh.b.siddha@...el.com,
	arjan@...ux.intel.com, ashok.raj@...el.com, shaohua.li@...el.com,
	davem@...emloft.net
Subject: Re: [Intel-IOMMU 02/10] Library routine for pre-allocat pool
 handling

On Mon, 11 Jun 2007 13:44:42 -0700
"Keshavamurthy, Anil S" <anil.s.keshavamurthy@...el.com> wrote:

> In the first implementation of ours, we had used mempools api's to 
> allocate memory and we were told that mempools with GFP_ATOMIC is
> useless and hence in the second implementation we came up with
> resource pools ( which is preallocate pools) and again as I understand
> the argument is why create another when we have slab allocation which
> is similar to this resource pools.

Odd.  mempool with GFP_ATOMIC is basically equivalent to your
resource-pools, isn't it?: we'll try the slab allocator and if that failed,
fall back to the reserves.

It's missing the recharge-from-a-kernel-thread functionality but that can be
added easily enough if it's useful.  It's slightly abusive of the mempool
philosophy, but it's probably better to do that than to create a new and
very-similar thing.

> Hence, can I assume that the conclusion of this 
> discussion is to use kmem_cache_alloc() functions 
> to allocate memory in dma_map_{single|sg} API's?
> 
> Again, if dma_map_{single|sg} API's fails due to 
> failure to allocate memory, the only thing that can
> be done is to panic as this is what few of the other 
> IOMMU implementation is doing today. 

If the only option is to panic then something's busted.  If it's network IO
then there should be a way of dropping the frame.  If it's disk IO then we
should report the failure and cause an IO error.

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