linux-kernel - Re: [Intel IOMMU 06/10] Avoid memory allocation failures in dma map api calls

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Date:	Wed, 20 Jun 2007 12:14:57 -0700
From:	Arjan van de Ven <arjan@...ux.intel.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	"Keshavamurthy, Anil S" <anil.s.keshavamurthy@...el.com>,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	ak@...e.de, gregkh@...e.de, muli@...ibm.com, ashok.raj@...el.com,
	davem@...emloft.net, clameter@....com
Subject: Re: [Intel IOMMU 06/10] Avoid memory allocation failures in	dma	map
 api calls

Peter Zijlstra wrote:
> So a reclaim context (kswapd and direct reclaim) set PF_MEMALLOC to
> ensure they themselves will not block on a memory allocation. And it is
> understood that these code paths have a bounded memory footprint.

that's a too simplistic view though; what happens is that kswapd will 
queue the IO, but the irq context will then take the IO from the queue 
and do the DMA mapping... which needs the memory.....
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