[PATCH] lockdep: core, reduce per-lock class-cache size
Ingo Molnar [Mon, 10 Jul 2006 11:44:04 +0000 (04:44 -0700)]
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>

include/linux/lockdep.h
kernel/lockdep.c

index 316e0fb..c040a8c 100644 (file)
@@ -120,7 +120,7 @@ struct lock_class {
  */
 struct lockdep_map {
        struct lock_class_key           *key;
-       struct lock_class               *class[MAX_LOCKDEP_SUBCLASSES];
+       struct lock_class               *class_cache;
        const char                      *name;
 };
 
index c1f34ad..9bad178 100644 (file)
@@ -1104,7 +1104,7 @@ extern void __error_too_big_MAX_LOCKDEP_SUBCLASSES(void);
  * 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 @@ register_lock_class(struct lockdep_map *lock, unsigned int subclass)
         */
        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 @@ register_lock_class(struct lockdep_map *lock, unsigned int subclass)
                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 @@ register_lock_class(struct lockdep_map *lock, unsigned int subclass)
 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 @@ void lockdep_init_map(struct lockdep_map *lock, const char *name,
        }
        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 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
                          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 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
                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_free_key_range(void *start, unsigned long size)
 
 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);
 }