2014-11-14 오전 10:24에 Laura Abbott 이(가) 쓴 글: > On 11/12/2014 11:18 PM, Gioh Kim wrote: >> Hi, >> >> I'm wondering why dma_alloc_coherent needs GFP_HIGHUSER | __GFP_ZERO flags >> in ion_cma_allocate(). >> >> I think dma_alloc_coherent can go to __dma_alloc if the system has CMA area. >> If __GFP_WAIT flag is set, it allocates memory from atomic pool. >> So I think calling dma_alloc_coherent with __GFP_WAIT is enough. >> >> And can I get zero-filled-memory from CMA if I set __GFP_ZERO? >> >> > > If we are actually using CMA, the GFP flags don't make much of a difference. > If > we didn't have CMA, using GFP_HIGHUSER would still be appropriate. The memory > is going to userspace so the user part is necessary and there should be no > need > for a lowmem mapping so highmem can be used. __GFP_ZERO might be redundant > since > the dma layer zeros memory anyway but it's probably safe.
If cma-heap can be created even-if the system doesn't have CMA area, you're right. But I think cma-heap should be created only if the system has CMA area. I think, in no CMA system, cma-heap creation and/or allocation from cma-heap should be failed, not allocate memory from lowmem or highmem as you say. Thanks for your reply. > > I think the flags should be fine as is. > > Thanks, > Laura > _______________________________________________ devel mailing list de...@linuxdriverproject.org http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
