On Fri, Jan 08, 2021 at 11:25:21AM -0800, Linus Torvalds wrote: > On Fri, Jan 8, 2021 at 9:53 AM Andrea Arcangeli <aarcange@xxxxxxxxxx> wrote: > > > > Do you intend to eventually fix the zygote vmsplice case or not? > > Because in current upstream it's not fixed currently using the > > enterprise default config. > > Is this the hugepage case? Neither of your patches actually touched > that, so I've forgotten the details. The two patches only fixed the TLB flushing deferral in clear_refs and uffd-wp. So I didn't actually try to fix the hugepage case by adding the page_count checks there too. I could try to do that at least it'd be consistent but I still would try to find an alternate solution later. > > Irrelevant special case as in: long term GUP pin on the memory? > > Irrelevant special case in that > > (a) an extra COW shouldn't be a correctness issue unless somebody > does something horribly wrong (and obviously the code that hasn't > taken the mmap_lock for writing are then examples of that) > > and > > (b) it's not a performance issue either unless you can find a real > load that does it. > > Hmm? For b) I don't have an hard time to imagine `ps` hanging for seconds, if clear_refs is touched on a 4T mm, but b) is not the main concern. Having to rely on a) is the main concern and it's not about tlb flushes but the long term GUP pins. Thanks, Andrea
