linux-kernel - Re: [PATCH] swiotlb: Fix inversed DMA_ATTR_NO

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Date:   Wed, 2 May 2018 16:31:09 +0200
From:   Michel Dänzer <michel@...nzer.net>
To:     Christoph Hellwig <hch@....de>, Daniel Vetter <daniel@...ll.ch>
Cc:     Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Christian König <christian.koenig@....com>,
        iommu@...ts.linux-foundation.org
Subject: Re: [PATCH] swiotlb: Fix inversed DMA_ATTR_NO_WARN test

On 2018-05-02 02:41 PM, Christoph Hellwig wrote:
> On Wed, May 02, 2018 at 02:18:56PM +0200, Daniel Vetter wrote:
>> Other dma-api backends like cma just shut up when __GFP_NOWARN is
>> passed. And afaiui Christoph Hellwig has plans to nuke the DMA_ATTR
>> stuff (or at least clean it up) - should we just remove
>> DMA_ATTR_NO_WARN and instead only look at __GFP_NOWARN?
> 
> No.  __GFP_NOWARN (and gfp_t flags in general) are the wrong interface
> for dma allocations and just cause problems.  I actually plan to
> get rid of the gfp_t argument in dma_alloc_attrs sooner, and only
> allow either GFP_KERNEL or GFP_DMA passed in dma_alloc_coherent.

How about GFP_TRANSHUGE_LIGHT? TTM uses that to opportunistically
allocate huge pages (GFP_TRANSHUGE can result in unacceptably long
delays with memory pressure).


-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer