Messages in this thread | | | Subject | Re: [PATCH v2 1/6] locking/lockdep: Track number of zapped classes | From | Bart Van Assche <> | Date | Mon, 13 Jan 2020 08:02:11 -0800 |
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On 1/13/20 6:58 AM, Waiman Long wrote: > On 1/13/20 9:55 AM, Peter Zijlstra wrote: >> On Mon, Dec 16, 2019 at 10:15:12AM -0500, Waiman Long wrote: >>> The whole point of the lockdep dynamic key patch is to allow unused >>> locks to be removed from the lockdep data buffers so that existing >>> buffer space can be reused. However, there is no way to find out how >>> many unused locks are zapped and so we don't know if the zapping process >>> is working properly. >>> >>> Add a new nr_zapped_classes variable to track that and show it in >>> /proc/lockdep_stats if it is non-zero. >>> >>> diff --git a/kernel/locking/lockdep_proc.c b/kernel/locking/lockdep_proc.c >>> index dadb7b7fba37..d98d349bb648 100644 >>> --- a/kernel/locking/lockdep_proc.c >>> +++ b/kernel/locking/lockdep_proc.c >>> @@ -336,6 +336,15 @@ static int lockdep_stats_show(struct seq_file *m, void *v) >>> seq_printf(m, " debug_locks: %11u\n", >>> debug_locks); >>> >>> + /* >>> + * Zappped classes and lockdep data buffers reuse statistics. >>> + */ >>> + if (!nr_zapped_classes) >>> + return 0; >>> + >>> + seq_puts(m, "\n"); >>> + seq_printf(m, " zapped classes: %11lu\n", >>> + nr_zapped_classes); >>> return 0; >>> } >> Why is that conditional? >> > Because I thought zapping class doesn't occur that often. Apparently, > class zapping happens when the system first boots up. I guess that > conditional check isn't needed. I can remove it in the next version.
Zapping a lock class happens every time a lock key is unregistered. That can happen any time as one can see in the following grep output:
$ git grep -lw 'lockdep_unregister_key' drivers/net/bonding/bond_main.c:4446: lockdep_unregister_key(&bond->stats_lock_key); drivers/net/team/team.c:1676: lockdep_unregister_key(&team->team_lock_key); drivers/net/team/team.c:1984: lockdep_unregister_key(&team->team_lock_key); include/linux/lockdep.h:294:extern void lockdep_unregister_key(struct lock_class_key *key); include/linux/lockdep.h:464:static inline void lockdep_unregister_key(struct lock_class_key *key) kernel/locking/lockdep.c:5166:void lockdep_unregister_key(struct lock_class_key *key) kernel/locking/lockdep.c:5201:EXPORT_SYMBOL_GPL(lockdep_unregister_key); kernel/workqueue.c:3456: lockdep_unregister_key(&wq->key); net/core/dev.c:9172: lockdep_unregister_key(&dev->qdisc_tx_busylock_key); net/core/dev.c:9173: lockdep_unregister_key(&dev->qdisc_running_key); net/core/dev.c:9174: lockdep_unregister_key(&dev->qdisc_xmit_lock_key); net/core/dev.c:9175: lockdep_unregister_key(&dev->addr_list_lock_key); net/core/dev.c:9183: lockdep_unregister_key(&dev->qdisc_xmit_lock_key); net/core/dev.c:9184: lockdep_unregister_key(&dev->addr_list_lock_key); tools/lib/lockdep/include/liblockdep/common.h:48:void lockdep_unregister_key(struct lock_class_key *key); tools/lib/lockdep/include/liblockdep/mutex.h:58: lockdep_unregister_key(&lock->key);
Bart.
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