* Andrea Arcangeli (aarca...@redhat.com) wrote: > The next suspect is the massive THP refcounting change that went > upstream recently:
> As further debug hint, can you try to disable THP and see if that > makes the problem go away? Yep, this seems to be the problem (cc'ing in Kirill). 122afea9626ab3f717b250a8dd3d5ebf57cdb56c - works (just before Kirill disables THP) 61f5d698cc97600e813ca5cf8e449b1ea1c11492 - breaks (when THP is reenabled) It's pretty reliable; as you say disabling THP makes it work again and putting it back to THP/madvise mode makes it break. And you need to test on a machine with some free ram to make sure THP has a chance to have happened. I'm not sure of all of the rework that happened in that series, but my reading of it is that splitting of THP pages gets deferred; so I wonder if when I do the madvise to turn THP off, if it's actually still got THP pages and thus we end up with a whole THP mapped when I'm expecting to be userfaulting those pages. Dave > > Thanks, > Andrea -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
