On Tue, Feb 23, 2016 at 2:32 AM, Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> wrote: > > I still worry about pmd_present(). It looks wrong to me. I wounder if > patch below makes a difference. Let's hope that's it, but in the meantime I do want to start the discussion about what to do if it isn't. We're at rc5, and 4.5 is just a few weeks away, and so far this issue hasn't gone anywhere. So the *good* scenario is that your pmd_present() patch fixes it, and we can all take a relieved breath. But if not, what then? It looks like we have two options: (a) do a (hopefully minimal) revert. I say "hopefully minimal", but I suspect the revert is going to have to undo pretty much all of the core THP changes. I'd hate to see that, because I really liked the cleanups. (b) mark THP as "depends on !S390" in the 4.5 release The (b) option is obviously much simpler, but it's a regression. I really don't like it, even if it generally shouldn't be the kind of regression that is actually user-noticeable (apart from performance). I also hate the fact that while the problem only seems to happen on s390, we don't even understand it, so maybe it's a more generic issue that for some reason just ends up being *much* more noticeable on one odd architecture that happens to be a bit different. I'm inclined to think of (b) as just a "give us more time to figure it out" thing, but I'm also worried that it will then make people not pursue this issue. How big is a revert patch that makes THP work on s390 again? Can we do a revert that keeps the infrastructure intact and makes it easy to revisit the THP cleanups later? Or is the revert inevitably going to be all the core patches in that series? Linus -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>