Hi Jason, On 09.10.2020 14:48, Jason Gunthorpe wrote: > On Fri, Oct 09, 2020 at 02:37:23PM +0200, Mauro Carvalho Chehab wrote: > >> I'm not a mm/ expert, but, from what I understood from Daniel's patch >> description is that this is unsafe *only if* __GFP_MOVABLE is used. > No, it is unconditionally unsafe. The CMA movable mappings are > specific VMAs that will have bad issues here, but there are other > types too. I'm trying to follow this thread, but I really wonder what do you mean by CMA movable mappings? If a buffer has been allocated from CMA and used for DMA, it won't be moved in the memory. It will stay at the same physical memory address all the time until freed by the owner. It just a matter of proper usage count tracking to delay freeing if it is still used somewhere. Best regards -- Marek Szyprowski, PhD Samsung R&D Institute Poland
