[$] The intersection of unstable pages and direct I/O

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.