On 17.05.23 12:19, Sumit Garg wrote:
On Wed, 17 May 2023 at 15:06, Christoph Hellwig <hch@xxxxxxxxxxxxx> 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
