Messages in this thread | | | Subject | Re: [PATCH v5 07/15] locking/lockdep: Free lock classes that are no longer in use | From | Bart Van Assche <> | Date | Thu, 10 Jan 2019 10:51:27 -0800 |
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On Thu, 2019-01-10 at 16:24 +0100, Peter Zijlstra wrote: > /* > * A data structure for delayed freeing of data structures that may be > - * accessed by RCU readers at the time these were freed. The size of the array > - * is a compromise between minimizing the amount of memory used by this array > - * and minimizing the number of wait_event() calls by get_pending_free_lock(). > + * accessed by RCU readers at the time these were freed. > */ > static struct pending_free { > - struct list_head zapped_classes; > struct rcu_head rcu_head; > + int index; > int pending; > -} pending_free[2]; > -static DECLARE_WAIT_QUEUE_HEAD(rcu_cb); > + struct list_head zapped[2]; > +} pending_free;
Hi Peter,
If the zapped[] array only has two elements there is no guarantee that an element will be free when zap_class() is called. I think we need at least num_online_cpus() elements to guarantee that at least one element is free when zap_class() is called. So removing the wait loop from get_pending_free_lock() seems wrong to me. Have you tried to run a workload that keeps all CPUs busy and that triggers get_pending_free_lock() frequently?
Thanks,
Bart.
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