On Wed, Jun 17, 2020 at 10:53:23AM -0700, Linus Torvalds wrote: > On Wed, Jun 17, 2020 at 8:49 AM Peter Xu <peterx@xxxxxxxxxx> wrote: > > > > I don't think it's a must, but mmap_sem should not be required at least by > > observing current code. E.g., do_user_addr_fault() of x86 does the accounting > > without mmap_sem even before this series. > > All the accounting should be per-thread and not need any locking. > > Which is why a remote GUP should never account to the remote mm - not > only isn't there an unambiguous thread to account to (an mm can share > many threads), but it would require locking not just for the remote > update, but for all normal page faults. But currently remote GUP will still do the page fault accounting on the remote task_struct, am I right? E.g., when the get_user_pages_remote() is called with "tsk != current", it seems the faultin_page() will still do maj_flt/min_flt accounting for that remote task/thread? Thanks, -- Peter Xu
