linux-kernel - Re: [PATCH] Make GFP_DMA allocations w/o ZONE

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Date:	Fri, 10 Jun 2011 10:12:33 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Dmitry Eremin-Solenikov <dbaryshkov@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	tglx@...utronix.de, rientjes@...gle.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, mel@....ul.ie,
	kamezawa.hiroyu@...fujitsu.com, riel@...hat.com, pavel@....cz
Subject: Re: [PATCH] Make GFP_DMA allocations w/o ZONE_DMA emit a warning
	instead of failing

On Fri, Jun 10, 2011 at 12:11:42PM +0400, Dmitry Eremin-Solenikov wrote:
> On 6/10/11, Andrew Morton <akpm@...ux-foundation.org> wrote:
> > On Fri, 10 Jun 2011 16:38:06 +0900 KOSAKI Motohiro
> > <kosaki.motohiro@...fujitsu.com> wrote:
> >
> >> Subject: [PATCH] Revert "mm: fail GFP_DMA allocations when ZONE_DMA is not
> >> configured"
> >
> > Confused.  We reverted this over a week ago.
> 
> Should one submit a patch adding a warning to GFP_DMA allocations
> w/o ZONE_DMA, or the idea of the original patch is wrong?

Linus was far from impressed by the original commit, saying:
| Using GFP_DMA is reasonable in a driver - on platforms where that
| matters, it should allocate from the DMA zone, on platforms where it
| doesn't matter it should be a no-op.

So no, not even a warning.

What is a useful exercise though is to remove GFP_DMA from those
allocations which should never have had GFP_DMA added - such as those
used for data structures which have nothing to do with DMA at all.
Also dma_alloc_coherent() should not be given GFP_DMA in any case.
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