On Mon, 2020-08-17 at 20:49 -0700, James Jones wrote: > On 8/17/20 8:18 AM, Brian Starkey wrote: > > Hi Ezequiel, > > > > On Sun, Aug 16, 2020 at 02:22:46PM -0300, Ezequiel Garcia wrote: > > > This heap is basically a wrapper around DMA-API dma_alloc_attrs, > > > which will allocate memory suitable for the given device. > > > > > > The implementation is mostly a port of the Contiguous Videobuf2 > > > memory allocator (see videobuf2/videobuf2-dma-contig.c) > > > over to the DMA-BUF Heap interface. > > > > > > The intention of this allocator is to provide applications > > > with a more system-agnostic API: the only thing the application > > > needs to know is which device to get the buffer for. > > > > > > Whether the buffer is backed by CMA, IOMMU or a DMA Pool > > > is unknown to the application. > > > > > > I'm not really expecting this patch to be correct or even > > > a good idea, but just submitting it to start a discussion on DMA-BUF > > > heap discovery and negotiation. > > > > > > > My initial reaction is that I thought dmabuf heaps are meant for use > > to allocate buffers for sharing across devices, which doesn't fit very > > well with having per-device heaps. > > > > For single-device allocations, would using the buffer allocation > > functionality of that device's native API be better in most > > cases? (Some other possibly relevant discussion at [1]) > > > > I can see that this can save some boilerplate for devices that want > > to expose private chunks of memory, but might it also lead to 100 > > aliases for the system's generic coherent memory pool? > > > > I wonder if a set of helpers to allow devices to expose whatever they > > want with minimal effort would be better. > > I'm rather interested on where this goes, as I was toying with using > some sort of heap ID as a basis for a "device-local" constraint in the > memory constraints proposals Simon and I will be discussing at XDC this > year. It would be rather elegant if there was one type of heap ID used > universally throughout the kernel that could provide a unique handle for > the shared system memory heap(s), as well as accelerator-local heaps on > fancy NICs, GPUs, NN accelerators, capture devices, etc. so apps could > negotiate a location among themselves. This patch seems to be a step > towards that in a way, but I agree it would be counterproductive if a > bunch of devices that were using the same underlying system memory ended > up each getting their own heap ID just because they used some SW > framework that worked that way. > > Would appreciate it if you could send along a pointer to your BoF if it > happens! > Here is it: https://linuxplumbersconf.org/event/7/contributions/818/ It would be great to see you there and discuss this, given I was hoping we could talk about how to meet a userspace allocator library expectations as well. Thanks, Ezequiel > Thanks, > -James > > > Cheers, > > -Brian > > > > 1. https://lore.kernel.org/dri-devel/57062477-30e7-a3de-6723-a50d03a402c4@xxxxxxxx/ > > > > > Given Plumbers is just a couple weeks from now, I've submitted > > > a BoF proposal to discuss this, as perhaps it would make > > > sense to discuss this live? > > > > > > Not-signed-off-by: Ezequiel Garcia <ezequiel@xxxxxxxxxxxxx>
