On 7/21/22 11:44, David Hildenbrand wrote:
Also, I*think* you can place pages via userfaultfd into shmem. Not sure if that would count "auto alloc", but it would certainly bypass fallocate().
Yeah, userfaultfd_register would probably have to forbid this for F_SEAL_AUTO_ALLOCATE vmas. Maybe the memfile_node can be reused for this, adding a new MEMFILE_F_NO_AUTO_ALLOCATE flags? Then userfault_register would do something like memfile_node_get_flags(vma->vm_file) and check the result.
This means moving this patch later, after "mm: Introduce memfile_notifier". Thanks, Paolo
