Longtime LWN readers will have encountered the concept of "stable pages" before; it was first covered here nearly 15 years ago. For the most part, the problem that stable pages were meant to solve — preventing errors when user space modifies a buffer that is under I/O — has been dealt with. But recent discussions show that there is one area where problems remain: direct I/O. There is some disagreement, though, over whether those problems are the result of user-space bugs and how much of a performance price should be paid to address them.