On Tue, May 22, 2018 at 03:13:58PM +0200, Christian König wrote: > 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? dma allocatr in this case: backends for dma_alloc_coherent/ dma_alloc_attrs. Most importantly dma_direct_alloc. But while we're at it I can't actually see any GFP_TRANSHUGE_LIGHT usage in TTM, just plain old GFP_TRANSHUGE. _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
