On Wed, May 17, 2023 at 08:23:33PM +0200, David Hildenbrand wrote: > In general: if user space controls it -> possibly forever -> long-term. Even > if in most cases it's a short delay: there is no trusting on user space. > > For example, iouring fixed buffers keep pages pinned until user space > decides to unregistered the buffers -> long-term. > > Short-term is, for example, something like O_DIRECT where we pin -> DMA -> > unpin in essentially one operation. Btw, one thing that's been on my mind is that I think we got the polarity on FOLL_LONGTERM wrong. Instead of opting into the long term behavior it really should be the default, with a FOLL_EPHEMERAL flag to opt out of it. And every users of this flag is required to have a comment explaining the life time rules for the pin..
