linux-kernel - Re: [Intel IOMMU 05/10] Intel IOMMU driver

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Message-Id: <20070625233249.c17c41c3.akpm@linux-foundation.org>
Date:	Mon, 25 Jun 2007 23:32:49 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Christoph Lameter <clameter@....com>
Cc:	"Keshavamurthy, Anil S" <anil.s.keshavamurthy@...el.com>,
	linux-kernel@...r.kernel.org, ak@...e.de, gregkh@...e.de,
	muli@...ibm.com, suresh.b.siddha@...el.com, arjan@...ux.intel.com,
	ashok.raj@...el.com, davem@...emloft.net
Subject: Re: [Intel IOMMU 05/10] Intel IOMMU driver

On Tue, 19 Jun 2007 16:32:23 -0700 (PDT) Christoph Lameter <clameter@....com> wrote:

> On Tue, 19 Jun 2007, Keshavamurthy, Anil S wrote:
> 
> > +static inline void *alloc_pgtable_page(void)
> > +{
> > +	return (void *)get_zeroed_page(GFP_ATOMIC);
> > +}
> 
> Need to pass gfp_t parameter. Repeates a couple of times.
> ...
> Is it not possible here to drop the lock and do the alloc with GFP_KERNEL 
> and deal with the resulting race? That is done in other parts of the 
> kernel.
> ...
> This may be able to become a GFP_KERNEL alloc since interrupts are enabled 
> at this point?
> ...
> GFP_KERNEL alloc possible?
> 

Yeah, if there are any callsites at all at which we know that we can
perform a sleeping allocation, Christoph's suggestions should be adopted. 
Because even a bare GFP_NOIO is heaps more robust than GFP_ATOMIC, and it
will also reload the free-pages reserves, making subsequent GFP_ATOMIC
allocations more likely to succeed.

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