On Mon, Oct 28, 2019 at 04:16:23PM +0300, Kirill A. Shutemov wrote: > I think active use of this feature will lead to performance degradation of > the system with time. > > Setting a single 4k page non-present in the direct mapping will require > splitting 2M or 1G page we usually map direct mapping with. And it's one > way road. We don't have any mechanism to map the memory with huge page > again after the application has freed the page. Right, we recently had a 'bug' where ftrace triggered something like this and facebook ran into it as a performance regression. So yes, this is a real concern.
