Hello, I am working on a DMA driver and noticed that consistent dma performs rapidly better than streaming dma. Since I want to employ zero copy dma I want to map the memory the driver allocates with dmam_alloc_coherent into the user process. I would like to implement this using IOCTL rather than mmap. I had a look at dma_mmap_attrs, which expects a vm_area struct. Is it ok to simply allocate one and fill it with apropriate data like in mmap_region(lxr.free-electrons.com/source/mm/mmap.c#L1594), if so I noticed that the kernel uses a memory pool (vm_area_cachep), which I apparently can't access (dmesg: Unknown symbol vm_area_cachep (err 0)), can I just wildly allocate or is there some black magic connected that relies on vma structs beeing in the area of the pool? I also looked at install_special_mapping which seems even closer to what I want to do (I do not need to provide a vma), however it is not exported as well. Is there a way to use it in a dynamic module anyway? I saw it used mainly in arch specific code. do_mmap, seems to have disappeared (at least it is not in any sane place in the 3.19 lxr), do_mmap_pgoff seems to be wrong for the job since I do not see how to tell that function that I have struct** page, rather than a file to back the mapping. I would greatly appreciate pointers on up to date summaries on the memory system, http://linux-mm.org/ seems slightly stale, https://www.kernel.org/doc/gorman/pdf/understand.pdf was helpful, although I could not entirly read it (yet). Any pointers to helpful functions, or gotchas are much appreciated. (I hope I managed to make it clear, that I tried to do my research + trial and lots of error...). Thanks, Malte _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
