linux-kernel - Re: [PATCH RFC] dma-direct: Try reallocation with GFP

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Message-ID: <s5hfu3qw659.wl-tiwai@suse.de>
Date:   Fri, 20 Apr 2018 11:58:58 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Christoph Hellwig <hch@....de>
Cc:     iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] dma-direct: Try reallocation with GFP_DMA32 if possible

On Fri, 20 Apr 2018 11:47:02 +0200,
Christoph Hellwig wrote:
> 
> On Mon, Apr 16, 2018 at 05:18:19PM +0200, Takashi Iwai wrote:
> > As the recent swiotlb bug revealed, we seem to have given up the
> > direct DMA allocation too early and felt back to swiotlb allocation.
> > The reason is that swiotlb allocator expected that dma_direct_alloc()
> > would try harder to get pages even below 64bit DMA mask with
> > GFP_DMA32, but the function doesn't do that but only deals with
> > GFP_DMA case.
> > 
> > This patch adds a similar fallback reallocation with GFP_DMA32 as
> > we've done with GFP_DMA.  The condition is that the coherent mask is
> > smaller than 64bit (i.e. some address limitation), and neither GFP_DMA
> > nor GFP_DMA32 is set beforehand.
> > 
> > Signed-off-by: Takashi Iwai <tiwai@...e.de>
> > 
> > ---
> > 
> > This is a resend of a test patch included in the previous thread
> > ("swiotlb: Fix unexpected swiotlb_alloc_coherent() failures").
> 
> I like the patch, but as-is it doesn't apply.  Can you resend it against
> latest Linus' tree?

It's because it's written on the tree with another fix patch I sent
beforehand ("[PATCH 1/2] dma-direct: Don't repeat allocation for no-op
GFP_DMA").

Could you check that one at first?  I'm fine to rebase and resubmit
this one, if still preferred, though.


thanks,

Takashi