On Tue, Jul 01, 2014 at 01:00:18PM +0200, Joerg Roedel wrote: > On Tue, Jul 01, 2014 at 09:29:49AM +0000, Gabbay, Oded wrote: > > In the KFD, we need to maintain a notion of each compute process. > > Therefore, we have an object called "kfd_process" that is created for > > each process that uses the KFD. Naturally, we need to be able to track > > the process's shutdown in order to perform cleanup of the resources it > > uses (compute queues, virtual address space, gpu local memory > > allocations, etc.). > > If it is only that, you can also use the task_exit notifier already in > the kernel. No task_exit will happen per thread not once per mm. > > > To enable this tracking mechanism, we decided to associate the > > kfd_process with mm_struct to ensure that a kfd_process object has > > exactly the same lifespan as the process it represents. We preferred to > > use the mm_struct and not a file description because using a file > > descriptor to track “process” shutdown is wrong in two ways: > > > > * Technical: file descriptors can be passed to unrelated processes using > > AF_UNIX sockets. This means that a process can exit while the file stays > > open. Even if we implement this “correctly” i.e. holding the address > > space & page tables alive until the file is finally released, it’s > > really dodgy. > > No, its not in this case. The file descriptor is used to connect a > process address space with a device context. Thus without the mappings > the file-descriptor is useless and the mappings should stay in-tact > until the fd is closed. > > It would be a very bad semantic for userspace if a fd that is passed on > fails on the other side because the sending process died. > Consider use case where there is no file associated with the mmu_notifier ie there is no device file descriptor that could hold and take care of mmu_notifier destruction and cleanup. We need this call chain for this case. Anyother idea than task_exit ? Cheers, Jérôme -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>