Re: [RFC][PATCH 1/3] locking/mutex: Rework mutex::owner

[Waiman Long]

On 08/23/2016 08:46 AM, Peter Zijlstra wrote:
  /*
   * Simple, straightforward mutexes with strict semantics:
@@ -48,13 +49,9 @@
   *   locks and tasks (and only those tasks)
   */
  struct mutex {
-       /* 1: unlocked, 0: locked, negative: locked, possible waiters */
-       atomic_t                count;
+       atomic_long_t           owner;
        spinlock_t              wait_lock;
        struct list_head        wait_list;
-#if defined(CONFIG_DEBUG_MUTEXES) || defined(CONFIG_MUTEX_SPIN_ON_OWNER)
-       struct task_struct      *owner;
-#endif
  #ifdef CONFIG_MUTEX_SPIN_ON_OWNER
        struct optimistic_spin_queue osq; /* Spinner MCS lock */
  #endif

I think you should put the wait_lock and osq next to each other to save 
8 bytes in space on 64-bit machines.

Cheers,
Longman