Yunsheng Lin [off-list ref] writes:

quoted

But, well, I'm not sure it is? You seem to be taking it as axiomatic
that the wait in itself is bad. Why? It's just a bit memory being held
on to while it is still in use, and so what?

Actually, I thought about adding some sort of timeout or kicking based on
jakub's waiting patch too.

But after looking at more caching in the networking, waiting and kicking/flushing
seems harder than recording the inflight pages, mainly because kicking/flushing
need very subsystem using page_pool owned page to provide a kicking/flushing
mechanism for it to work, not to mention how much time does it take to do all
the kicking/flushing.

Eliding the details above, but yeah, you're right, there are probably
some pernicious details to get right if we want to flush all caches. S
I wouldn't do that to start with. Instead, just add the waiting to start
with, then wait and see if this actually turns out to be a problem in
practice. And if it is, identify the source of that problem, deal with
it, rinse and repeat :)

-Toke