Date: Wed, 20 Jun 2007 10:30:38 -0700
From: "Siddha, Suresh B" <suresh.b.siddha@intel.com>
To: Arjan van de Ven <arjan@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
       "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, suresh.b.siddha@intel.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
Message-ID: <20070620173038.GA25516@linux-os.sc.intel.com>
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>
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On Wed, Jun 20, 2007 at 06:03:02AM -0700, Arjan van de Ven wrote:
> Peter Zijlstra wrote:
> >
> >
> >PF_MEMALLOC as is, is meant to salvage the VM from the typical VM
> >deadlock. 
> 
> .. and this IS the typical VM deadlock.. it is your storage driver 
> trying to write out a piece of memory on behalf of the VM, and calls 
> the iommu to map it, which then needs a bit of memory....

Today PF_MEMALLOC doesn't do much in interrupt context. If PF_MEMALLOC
is the right usage model for this, then we need to fix the behavior of
PF_MEMALLOC in the interrupt context(for our usage model, we do most
of the allocations in interrupt context).

I am not very familiar with PF_MEMALLOC. So experts please comment.

thanks,
suresh
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