[PATCH] lockdep: core, reduce per-lock class-cache size
lockdep_map is embedded into every lock, which blows up data structure
sizes all around the kernel. Reduce the class-cache to be for the default
class only - that is used in 99.9% of the cases and even if we dont have a
class cached, the lookup in the class-hash is lockless.
This change reduces the per-lock dep_map overhead by 56 bytes on 64-bit
platforms and by 28 bytes on 32-bit platforms.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 316e0fb..c040a8c 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -120,7 +120,7 @@
*/
struct lockdep_map {
struct lock_class_key *key;
- struct lock_class *class[MAX_LOCKDEP_SUBCLASSES];
+ struct lock_class *class_cache;
const char *name;
};
diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index c1f34ad..9bad178 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -1104,7 +1104,7 @@
* itself, so actual lookup of the hash should be once per lock object.
*/
static inline struct lock_class *
-register_lock_class(struct lockdep_map *lock, unsigned int subclass)
+look_up_lock_class(struct lockdep_map *lock, unsigned int subclass)
{
struct lockdep_subclass_key *key;
struct list_head *hash_head;
@@ -1148,7 +1148,26 @@
*/
list_for_each_entry(class, hash_head, hash_entry)
if (class->key == key)
- goto out_set;
+ return class;
+
+ return NULL;
+}
+
+/*
+ * Register a lock's class in the hash-table, if the class is not present
+ * yet. Otherwise we look it up. We cache the result in the lock object
+ * itself, so actual lookup of the hash should be once per lock object.
+ */
+static inline struct lock_class *
+register_lock_class(struct lockdep_map *lock, unsigned int subclass)
+{
+ struct lockdep_subclass_key *key;
+ struct list_head *hash_head;
+ struct lock_class *class;
+
+ class = look_up_lock_class(lock, subclass);
+ if (likely(class))
+ return class;
/*
* Debug-check: all keys must be persistent!
@@ -1163,6 +1182,9 @@
return NULL;
}
+ key = lock->key->subkeys + subclass;
+ hash_head = classhashentry(key);
+
__raw_spin_lock(&hash_lock);
/*
* We have to do the hash-walk again, to avoid races
@@ -1209,8 +1231,8 @@
out_unlock_set:
__raw_spin_unlock(&hash_lock);
-out_set:
- lock->class[subclass] = class;
+ if (!subclass)
+ lock->class_cache = class;
DEBUG_LOCKS_WARN_ON(class->subclass != subclass);
@@ -1914,7 +1936,7 @@
}
lock->name = name;
lock->key = key;
- memset(lock->class, 0, sizeof(lock->class[0])*MAX_LOCKDEP_SUBCLASSES);
+ lock->class_cache = NULL;
}
EXPORT_SYMBOL_GPL(lockdep_init_map);
@@ -1928,8 +1950,8 @@
unsigned long ip)
{
struct task_struct *curr = current;
+ struct lock_class *class = NULL;
struct held_lock *hlock;
- struct lock_class *class;
unsigned int depth, id;
int chain_head = 0;
u64 chain_key;
@@ -1947,8 +1969,11 @@
return 0;
}
- class = lock->class[subclass];
- /* not cached yet? */
+ if (!subclass)
+ class = lock->class_cache;
+ /*
+ * Not cached yet or subclass?
+ */
if (unlikely(!class)) {
class = register_lock_class(lock, subclass);
if (!class)
@@ -2449,48 +2474,44 @@
void lockdep_reset_lock(struct lockdep_map *lock)
{
- struct lock_class *class, *next, *entry;
+ struct lock_class *class, *next;
struct list_head *head;
unsigned long flags;
int i, j;
raw_local_irq_save(flags);
- __raw_spin_lock(&hash_lock);
/*
- * Remove all classes this lock has:
+ * Remove all classes this lock might have:
*/
+ for (j = 0; j < MAX_LOCKDEP_SUBCLASSES; j++) {
+ /*
+ * If the class exists we look it up and zap it:
+ */
+ class = look_up_lock_class(lock, j);
+ if (class)
+ zap_class(class);
+ }
+ /*
+ * Debug check: in the end all mapped classes should
+ * be gone.
+ */
+ __raw_spin_lock(&hash_lock);
for (i = 0; i < CLASSHASH_SIZE; i++) {
head = classhash_table + i;
if (list_empty(head))
continue;
list_for_each_entry_safe(class, next, head, hash_entry) {
- for (j = 0; j < MAX_LOCKDEP_SUBCLASSES; j++) {
- entry = lock->class[j];
- if (class == entry) {
- zap_class(class);
- lock->class[j] = NULL;
- break;
- }
+ if (unlikely(class == lock->class_cache)) {
+ __raw_spin_unlock(&hash_lock);
+ DEBUG_LOCKS_WARN_ON(1);
+ goto out_restore;
}
}
}
-
- /*
- * Debug check: in the end all mapped classes should
- * be gone.
- */
- for (j = 0; j < MAX_LOCKDEP_SUBCLASSES; j++) {
- entry = lock->class[j];
- if (!entry)
- continue;
- __raw_spin_unlock(&hash_lock);
- DEBUG_LOCKS_WARN_ON(1);
- raw_local_irq_restore(flags);
- return;
- }
-
__raw_spin_unlock(&hash_lock);
+
+out_restore:
raw_local_irq_restore(flags);
}
