On Thu, Jan 07, 2021 at 01:05:19PM -0800, Linus Torvalds wrote: > I think those would very much be worth fixing, so that if > UFFDIO_WRITEPROTECT taking the mmapo_sem for writing causes problems, > we can _fix_ those problems. > > But I think it's entirely wrong to treat UFFDIO_WRITEPROTECT as > specially as Andrea seems to want to treat it. Particularly with > absolutely zero use cases to back it up. Again for the record: there's nothing at all special in UFFDIO_WRITEPROTECT in this respect. If you could stop mentioning UFFDIO_WRITEPROTECT and only focus on softdirty/clear_refs, maybe you wouldn't think my judgment is biased towards clear_refs/softdirty too. You can imagine the side effects of page_count doing a COW erroneously, as corollary of the fact that KSM won't ever allow to merge two pages if one of them is under GUP pin. Why is that? Thanks, Andrea
