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

[Peter Zijlstra]

On Tue, Aug 23, 2016 at 04:17:54PM -0400, Waiman Long wrote:
> 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.

Right you are.. didn't get around to looking at layout yet. Just barely
got it to compile and boot :-)