From: Mel Gorman <mgorman@techsingularity.net>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Qais Yousef <qais.yousef@imgtec.com>,
linux-mips@linux-mips.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, ralf@linux-mips.org
Subject: Re: [PATCH] MIPS: Fix DMA contiguous allocation
Date: Wed, 9 Dec 2015 11:36:35 +0000 [thread overview]
Message-ID: <20151209113635.GA15910@techsingularity.net> (raw)
In-Reply-To: <20151208141939.d0edbb72b3c15844c5ac25ea@linux-foundation.org>
On Tue, Dec 08, 2015 at 02:19:39PM -0800, Andrew Morton wrote:
> On Tue, 8 Dec 2015 10:18:50 +0000 Qais Yousef <qais.yousef@imgtec.com> wrote:
>
> > Recent changes to how GFP_ATOMIC is defined seems to have broken the condition
> > to use mips_alloc_from_contiguous() in mips_dma_alloc_coherent().
> >
> > I couldn't bottom out the exact change but I think it's this one
> >
> > d0164adc89f6 (mm, page_alloc: distinguish between being unable to sleep,
> > unwilling to sleep and avoiding waking kswapd)
> >
> > >From what I see GFP_ATOMIC has multiple bits set and the check for !(gfp
> > & GFP_ATOMIC) isn't enough. To verify if the flag is atomic we need to make
> > sure that (gfp & GFP_ATOMIC) == GFP_ATOMIC to verify that all bits rquired to
> > satisfy GFP_ATOMIC condition are set.
> >
> > ...
> >
> > --- a/arch/mips/mm/dma-default.c
> > +++ b/arch/mips/mm/dma-default.c
> > @@ -145,7 +145,7 @@ static void *mips_dma_alloc_coherent(struct device *dev, size_t size,
> >
> > gfp = massage_gfp_flags(dev, gfp);
> >
> > - if (IS_ENABLED(CONFIG_DMA_CMA) && !(gfp & GFP_ATOMIC))
> > + if (IS_ENABLED(CONFIG_DMA_CMA) && ((gfp & GFP_ATOMIC) != GFP_ATOMIC))
> > page = dma_alloc_from_contiguous(dev,
> > count, get_order(size));
> > if (!page)
>
> hm. It seems that the code is asking "can I do a potentially-sleeping
> memory allocation"?
>
> The way to do that under the new regime is
>
> if (IS_ENABLED(CONFIG_DMA_CMA) && gfpflags_allow_blocking(gfp))
>
> Mel, can you please confirm?
Yes, this is the correct way it should be checked. The full flags cover
watermark and kswapd treatment which potentially could be altered by
the caller.
--
Mel Gorman
SUSE Labs
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next prev parent reply other threads:[~2015-12-09 11:36 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-12-08 10:18 Qais Yousef
2015-12-08 12:12 ` Sergei Shtylyov
2015-12-08 22:19 ` Andrew Morton
2015-12-09 11:36 ` Mel Gorman [this message]
2015-12-09 14:32 ` Qais Yousef
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