Re: [PATCH 00/14] replace call_rcu by kfree_rcu for simple kmem_cache_free callback

Jason A. Donenfeld
2024-06-17T16:33:40Z

On Mon, Jun 17, 2024 at 6:30 PM Uladzislau Rezki <urezki@gmail.com> wrote:
> Here if an "err" is less then "0" means there are still objects
> whereas "is_destroyed" is set to "true" which is not correlated
> with a comment:
>
> "Destruction happens when no objects"

The comment is just poorly written. But the logic of the code is right.

>
> > out_unlock:
> > mutex_unlock(&slab_mutex);
> > cpus_read_unlock();
> > diff --git a/mm/slub.c b/mm/slub.c
> > index 1373ac365a46..7db8fe90a323 100644
> > --- a/mm/slub.c
> > +++ b/mm/slub.c
> > @@ -4510,6 +4510,8 @@ void kmem_cache_free(struct kmem_cache *s, void *x)
> > return;
> > trace_kmem_cache_free(_RET_IP_, x, s);
> > slab_free(s, virt_to_slab(x), x, _RET_IP_);
> > + if (s->is_destroyed)
> > + kmem_cache_destroy(s);
> > }
> > EXPORT_SYMBOL(kmem_cache_free);
> >
> > @@ -5342,9 +5344,6 @@ static void free_partial(struct kmem_cache *s, struct kmem_cache_node *n)
> > if (!slab->inuse) {
> > remove_partial(n, slab);
> > list_add(&slab->slab_list, &discard);
> > - } else {
> > - list_slab_objects(s, slab,
> > - "Objects remaining in %s on __kmem_cache_shutdown()");
> > }
> > }
> > spin_unlock_irq(&n->list_lock);
> >
> Anyway it looks like it was not welcome to do it in the kmem_cache_free()
> function due to performance reason.

"was not welcome" - Vlastimil mentioned *potential* performance
concerns before I posted this. I suspect he might have a different
view now, maybe?

Vlastimil, this is just checking a boolean (which could be
unlikely()'d), which should have pretty minimal overhead. Is that
alright with you?

Jason