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

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Message-ID: <20070620173038.GA25516@linux-os.sc.intel.com>
Date:	Wed, 20 Jun 2007 10:30:38 -0700
From:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>
To:	Arjan van de Ven <arjan@...ux.intel.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	"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,
	suresh.b.siddha@...el.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

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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