Messages in this thread | | | Subject | Re: [PATCH] swiotlb: Fix inversed DMA_ATTR_NO_WARN test | From | Christian König <> | Date | Tue, 22 May 2018 15:13:58 +0200 |
| |
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.
| |