On Fri, Aug 10, 2018 at 3:29 AM Vlad Buslov <vla...@mellanox.com> wrote: > > Approach you suggest is valid, but has its own trade-offs: > > - As you noted, lock granularity becomes coarse-grained due to per-netns > scope.
Sure, you acquire idrinfo->lock too, the only difference is how long you take it. The bottleneck of your approach is the same, also you take idrinfo->lock twice, so the contention is heavier. > > - I am not sure it is possible to call idr_replace() without obtaining > idrinfo->lock in this particular case. Concurrent delete of action with > same id is possible and, according to idr_replace() description, > unlocked execution is not supported for such use-case: But we can hold its refcnt before releasing idrinfo->lock, so idr_replace() can't race with concurrent delete. > > - High rate or replace request will generate a lot of unnecessary memory > allocations and deallocations. > Yes, this is literally how RCU works, always allocate and copy, release upon error. Also, if this is really a problem, we have SLAB_TYPESAFE_BY_RCU too. ;)
