[Devel] Re: [-mm PATCH 6/9] Memory controller add per container LRU and reclaim (v4)

[Peter Zijlstra]

On Mon, 2007-07-30 at 19:07 +0530, Dhaval Giani wrote:
> Hi Balbir,
> 
> > diff -puN mm/memcontrol.c~mem-control-lru-and-reclaim mm/memcontrol.c
> > --- linux-2.6.23-rc1-mm1/mm/memcontrol.c~mem-control-lru-and-reclaim	2007-07-28 01:12:50.000000000 +0530
> > +++ linux-2.6.23-rc1-mm1-balbir/mm/memcontrol.c	2007-07-28 01:12:50.000000000 +0530
>  
> >  /*
> >   * The memory controller data structure. The memory controller controls both
> > @@ -51,6 +54,10 @@ struct mem_container {
> >  	 */
> >  	struct list_head active_list;
> >  	struct list_head inactive_list;
> > +	/*
> > +	 * spin_lock to protect the per container LRU
> > +	 */
> > +	spinlock_t lru_lock;
> >  };
> 
> The spinlock is not annotated by lockdep. The following patch should do
> it.

One does not need explicit lockdep annotations unless there is a non
obvious use of the locks. A typical example of that would be the inode
locks, that get placed differently in the various filesystem's locking
hierarchy and might hence seem to generate contradictory locking rules -
even though they are consistent within a particular filesystem.

So unless there are 2 or more distinct locking hierarchies this one lock
partakes in, there is no need for this annotation.

Was this patch driven by a lockdep report?

> Signed-off-by: Dhaval Giani <dhaval at linux.vnet.ibm.com>
> Signed-off-by: Gautham Shenoy R <ego at in.ibm.com>
> 
> 
> Index: linux-2.6.23-rc1/mm/memcontrol.c
> ===================================================================
> --- linux-2.6.23-rc1.orig/mm/memcontrol.c	2007-07-30 17:27:24.000000000 +0530
> +++ linux-2.6.23-rc1/mm/memcontrol.c	2007-07-30 18:43:40.000000000 +0530
> @@ -501,6 +501,9 @@
>  
>  static struct mem_container init_mem_container;
>  
> +/* lockdep should know about lru_lock */
> +static struct lock_class_key lru_lock_key;
> +
>  static struct container_subsys_state *
>  mem_container_create(struct container_subsys *ss, struct container *cont)
>  {
> @@ -519,6 +522,7 @@
>  	INIT_LIST_HEAD(&mem->active_list);
>  	INIT_LIST_HEAD(&mem->inactive_list);
>  	spin_lock_init(&mem->lru_lock);
> +	lockdep_set_class(&mem->lru_lock, &lru_lock_key);
>  	mem->control_type = MEM_CONTAINER_TYPE_ALL;
>  	return &mem->css;
>  }
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