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

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Date:	Mon, 8 Sep 2008 13:41:19 +0200
From:	Joerg Roedel <joerg.roedel@....com>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
CC:	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 Sat, Sep 06, 2008 at 09:18:37PM +0900, FUJITA Tomonori wrote:
> 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;

Ok, so please add a comment to this so we know in the future why this is
there.

Joerg

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