On Fri, Jun 9, 2023 at 1:42 PM Peter Xu <peterx@xxxxxxxxxx> wrote: > > On Thu, Jun 08, 2023 at 05:51:56PM -0700, Suren Baghdasaryan wrote: > > migration_entry_wait does not need VMA lock, therefore it can be dropped > > before waiting. Introduce VM_FAULT_VMA_UNLOCKED to indicate that VMA > > lock was dropped while in handle_mm_fault(). > > Note that once VMA lock is dropped, the VMA reference can't be used as > > there are no guarantees it was not freed. > > Then vma lock behaves differently from mmap read lock, am I right? Can we > still make them match on behaviors, or there's reason not to do so? I think we could match their behavior by also dropping mmap_lock here when fault is handled under mmap_lock (!(fault->flags & FAULT_FLAG_VMA_LOCK)). I missed the fact that VM_FAULT_COMPLETED can be used to skip dropping mmap_lock in do_page_fault(), so indeed, I might be able to use VM_FAULT_COMPLETED to skip vma_end_read(vma) for per-vma locks as well instead of introducing FAULT_FLAG_VMA_LOCK. I think that was your idea of reusing existing flags? > > One reason is if they match they can reuse existing flags and there'll be > less confusing, e.g. this: > > (fault->flags & FAULT_FLAG_VMA_LOCK) && > (vm_fault_ret && (VM_FAULT_RETRY || VM_FAULT_COMPLETE)) > > can replace the new flag, iiuc. > > Thanks, > > -- > Peter Xu > > -- > To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@xxxxxxxxxxx. >
