On Thu, Sep 12, 2024 at 06:16:56PM +0200, Uladzislau Rezki wrote: > On Wed, Sep 11, 2024 at 03:39:19AM -0700, Paul E. McKenney wrote: > > On Wed, Sep 11, 2024 at 11:43:54AM +0200, Uladzislau Rezki wrote: > > > On Tue, Sep 10, 2024 at 08:42:54AM -0700, Paul E. McKenney wrote: > > > > On Tue, Aug 20, 2024 at 05:59:35PM +0200, Uladzislau Rezki (Sony) wrote: > > > > > Add a kvfree_rcu_barrier() function. It waits until all > > > > > in-flight pointers are freed over RCU machinery. It does > > > > > not wait any GP completion and it is within its right to > > > > > return immediately if there are no outstanding pointers. > > > > > > > > > > This function is useful when there is a need to guarantee > > > > > that a memory is fully freed before destroying memory caches. > > > > > For example, during unloading a kernel module. > > > > > > > > > > Signed-off-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx> > > > > > Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx> > > > > > > > > As a follow-on patch, once kvfree_rcu_barrier() is accepted into > > > > mainline, should we add a call to kvfree_rcu_barrier() to the > > > > rcu_barrier_throttled() function in kernel/rcu/tree.c? > > > > > > > > This would allow the do_rcu_barrier module parameter to be used to clear > > > > out kfree_rcu() as well as call_rcu() work. This would be useful to > > > > people running userspace benchmarks that cause the kernel to do a lot > > > > of kfree_rcu() calls. Always good to avoid messing up the results from > > > > the current run due to deferred work from the previous run. Even better > > > > would be to actually account for the deferred work, but do_rcu_barrier > > > > can help with that as well. ;-) > > > > > > > > Thoughts? > > > > > > > Makes sense. To be make sure that all objects are flushed. And as you > > > mentioned it is good to have it for benchmarking as a return to a baseline > > > point. > > > > > > One issue is probably a "name" which would be common for both: > > > > > > rcu_barrier() > > > kvfree_rcu_barrier() > > > > > > i mean /sys/module/rcutree/parameters/do_rcu_barrier. From how i > > > would see it, it is supposed to trigger just rcu_barrier() API. > > > > One approach would be to keep the old functionality, but create > > a new sysfs variable that does both. Except that to avoid code > > duplication, we would likely end up with both actually doing > > both. > > > > Another approach is to rename the sysfs variable. This might > > work if there are not too many people using it. Might. ;-) > > > > Other approaches? > > > Maybe just rename from/to: do_rcu_barrier -> do_barrier? Probably this > would be the best, but as you noted, there might be users :) > > To be safe, we can add kvfree_rcu_barrier() to the rcu_barrier_throttled() and > document that it does both now! That does sound safest to me. We just might find that our users (if any) expected that it already did both. ;-) Thanx, Paul
