On Wed, Dec 23, 2020 at 05:21:43PM -0800, Andy Lutomirski wrote: > I don’t love this as a long term fix. AFAICT we can have mm_tlb_flush_pending > set for quite a while — mprotect seems like it can wait in IO while splitting > a huge page, for example. That gives us a window in which every write fault > turns into a TLB flush.
mprotect can't run concurrently with a page fault in the first place. One other near zero cost improvement easy to add if this would be "if (vma->vm_flags & (VM_SOFTDIRTY|VM_UFFD_WP))" and it could be made conditional to the two config options too. Still I don't mind doing it in some other way, uffd-wp has much easier time doing it in another way in fact. Whatever performs better is fine, but queuing up pending invalidate ranges don't look very attractive since it'd be a fixed cost that we'd always have to pay even when there's no fault (and there can't be any fault at least for mprotect). Thanks, Andrea
