Am 02.05.2018 um 18:59 schrieb Michel Dänzer:
On 2018-05-02 06:21 PM, Christoph Hellwig wrote:
On Wed, May 02, 2018 at 04:31:09PM +0200, Michel Dänzer wrote:
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).
Well, that is exactly what I don't want drivers to do - same for
__GFP_COMP in some drm code. This very much assumes the page allocator
is used to back dma allocations, which very often it actually isn't, and
any use of magic gfp flags creates a tight coupling of consumers with a
specific implementation.
In general I can't think of a good reason not to actually use
GFP_TRANSHUGE_LIGHT by default in the dma allocator unless
DMA_ATTR_ALLOC_SINGLE_PAGES is set. Can you prepare a patch for that?
I'm afraid I'll have to leave that to somebody else.
Coming back to this topic once more, sorry for the delay but busy as
usual :)
What exactly do you mean with "dma allocator" here? The TTM allocator
using the dma_alloc_coherent calls? Or the swiotlb implementation of the
calls?
Christian.
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