Message-ID: <46797CB1.8070008@linux.intel.com>
Date: Wed, 20 Jun 2007 12:14:57 -0700
From: Arjan van de Ven <arjan@linux.intel.com>
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To: Peter Zijlstra <peterz@infradead.org>
CC: "Siddha, Suresh B" <suresh.b.siddha@intel.com>,
       "Keshavamurthy, Anil S" <anil.s.keshavamurthy@intel.com>,
       akpm@linux-foundation.org, linux-kernel@vger.kernel.org, ak@suse.de,
       gregkh@suse.de, muli@il.ibm.com, ashok.raj@intel.com,
       davem@davemloft.net, clameter@sgi.com
Subject: Re: [Intel IOMMU 06/10] Avoid memory allocation failures in	dma	map
 api calls
References: <20070619213701.219910000@askeshav-devel.jf.intel.com>	 <20070619213808.798646000@askeshav-devel.jf.intel.com>	 <1182326799.21117.19.camel@twins> <46792586.20706@linux.intel.com>	 <20070620173038.GA25516@linux-os.sc.intel.com> <1182362703.21117.79.camel@twins>
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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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