On Thu, 18 May 2023 at 09:51, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: > > 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.. It does look like a better approach to me given the very nature of user space pages. -Sumit
