On 26/01/21 23:02, Sean Christopherson wrote:
You can do the deferred freeing with a short write-side critical section to
ensure all readers have terminated.
Hmm, the most obvious downside I see is that the zap_collapsible_sptes() case
will not scale as well as the RCU approach. E.g. the lock may be heavily
contested when refaulting all of guest memory to (re)install huge pages after a
failed migration.
The simplest solution is to use a write_trylock on the read_unlock()
path; if it fails, schedule a delayed work item 1 second in the future
so that it's possible to do some batching.
(The work item would also have to re-check the llist after each iteration.)
Paolo
