Messages in this thread | | | Date | Wed, 17 May 2023 20:23:33 +0200 | Subject | Re: [PATCH] tee: add FOLL_LONGTERM for CMA case when alloc shm | From | David Hildenbrand <> |
| |
On 17.05.23 12:19, Sumit Garg wrote: > On Wed, 17 May 2023 at 15:06, Christoph Hellwig <hch@infradead.org> wrote: >> >> On Wed, May 17, 2023 at 02:56:13PM +0530, Sumit Garg wrote: >>> Do you mean a pinned user-space page can be paged out automatically? >> >> No, pinned pages can't be paged out. >> >> But a short term pin implies it will be release after a short delay, >> and it is feasible for wait for the pin to go away. > > Okay, I see. I would be interested to know the ranges for that short > delay. I guess it may depend on how much memory pressure there is... >
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.
-- Thanks,
David / dhildenb
| |