On Tue, Jun 18, 2024 at 11:31:00AM +0200, Uladzislau Rezki wrote: > > On 6/17/24 8:42 PM, Uladzislau Rezki wrote: > > >> + > > >> + s = container_of(work, struct kmem_cache, async_destroy_work); > > >> + > > >> + // XXX use the real kmem_cache_free_barrier() or similar thing here > > > It implies that we need to introduce kfree_rcu_barrier(), a new API, which i > > > wanted to avoid initially. > > > > I wanted to avoid new API or flags for kfree_rcu() users and this would > > be achieved. The barrier is used internally so I don't consider that an > > API to avoid. How difficult is the implementation is another question, > > depending on how the current batching works. Once (if) we have sheaves > > proven to work and move kfree_rcu() fully into SLUB, the barrier might > > also look different and hopefully easier. So maybe it's not worth to > > invest too much into that barrier and just go for the potentially > > longer, but easier to implement? > > > Right. I agree here. If the cache is not empty, OK, we just defer the > work, even we can use a big 21 seconds delay, after that we just "warn" > if it is still not empty and leave it as it is, i.e. emit a warning and > we are done. > > Destroying the cache is not something that must happen right away. OK, I have to ask... Suppose that the cache is created and destroyed by a module and init/cleanup time, respectively. Suppose that this module is rmmod'ed then very quickly insmod'ed. Do we need to fail the insmod if the kmem_cache has not yet been fully cleaned up? If not, do we have two versions of the same kmem_cache in /proc during the overlap time? Thanx, Paul > > > Since you do it asynchronous can we just repeat > > > and wait until it a cache is furry freed? > > > > The problem is we want to detect the cases when it's not fully freed > > because there was an actual read. So at some point we'd need to stop the > > repeats because we know there can no longer be any kfree_rcu()'s in > > flight since the kmem_cache_destroy() was called. > > > Agree. As noted above, we can go with 21 seconds(as an example) interval > and just perform destroy(without repeating). > > -- > Uladzislau Rezki
