linux-kernel - Re: [PATCH] x86: use __GFP_NORETRY in the case of GFP

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Message-Id: <20080906211813F.fujita.tomonori@lab.ntt.co.jp>
Date:	Sat, 6 Sep 2008 21:18:37 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	joerg.roedel@....com
Cc:	fujita.tomonori@....ntt.co.jp, mingo@...hat.com,
	linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org
Subject: Re: [PATCH] x86: use __GFP_NORETRY in the case of GFP_DMA with
 pci-nommu

On Fri, 5 Sep 2008 12:43:05 +0200
Joerg Roedel <joerg.roedel@....com> wrote:

> On Fri, Sep 05, 2008 at 05:58:48PM +0900, FUJITA Tomonori wrote:
> > Signed-off-by: FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
> > ---
> >  arch/x86/kernel/pci-nommu.c |    3 +++
> >  1 files changed, 3 insertions(+), 0 deletions(-)
> > 
> > diff --git a/arch/x86/kernel/pci-nommu.c b/arch/x86/kernel/pci-nommu.c
> > index 526b2db..3495f88 100644
> > --- a/arch/x86/kernel/pci-nommu.c
> > +++ b/arch/x86/kernel/pci-nommu.c
> > @@ -102,6 +102,9 @@ nommu_alloc_coherent(struct device *hwdev, size_t size,
> >  	if (dma_mask == DMA_24BIT_MASK)
> >  		gfp |= GFP_DMA;
> >  again:
> > +	if (gfp & GFP_DMA)
> > +		gfp |= __GFP_NORETRY;
> > +
> 
> Huh? Why that? The __GFP_NORETRY is a hint from the caller to the page
> allocator on how aggressive it should try to allocate memory. I don't
> think the DMA code should touch those flags unless there is a very very
> good reason for it.

The current comment is reasonable for me:

/* Don't invoke OOM killer or retry in lower 16MB DMA zone */
if (gfp & __GFP_DMA)
     noretry = 1;
--
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