On Wed, May 08, 2024 at 04:44:32PM +0100, Pavel Begunkov wrote:
like a weird and indirect way to get there. Why can't io_uring just be the entity that does the final free and not mess with the logic allocator?
Then the user has to do a syscall (e.g. via io_uring) to return pages, and there we'd need to care how to put the pages efficiently, i.e. hitting the page pool's fast path, e.g. by hoping napi is scheduled and scheduled for the CPU we're running on, or maybe transferring the pages to the right CPU first.
Compare it with userspace putting pages into a ring, and the allocator taking from there when needed without any extra synchronisation and hassle just because it's a sole consumer.
Wow, that sounds a bit terrifying for security, but I guess I can see your point.
You are replacing the whole allocator logic if you are effectively putting the free list in userspace memory.
Jason