Re: [PATCH 3/12] ksm: pages_unshared and pages_volatile

[Andrew Morton <akpm@linux-foundation.org>]

On Mon, 3 Aug 2009 13:11:53 +0100 (BST)
Hugh Dickins <hugh.dickins@tiscali.co.uk> wrote:

> The pages_shared and pages_sharing counts give a good picture of how
> successful KSM is at sharing; but no clue to how much wasted work it's
> doing to get there.  Add pages_unshared (count of unique pages waiting
> in the unstable tree, hoping to find a mate) and pages_volatile.
> 
> pages_volatile is harder to define.  It includes those pages changing
> too fast to get into the unstable tree, but also whatever other edge
> conditions prevent a page getting into the trees: a high value may
> deserve investigation.  Don't try to calculate it from the various
> conditions: it's the total of rmap_items less those accounted for.
> 
> Also show full_scans: the number of completed scans of everything
> registered in the mm list.
> 
> The locking for all these counts is simply ksm_thread_mutex.
> 
> ...
>
>  static inline struct rmap_item *alloc_rmap_item(void)
>  {
> -	return kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL);
> +	struct rmap_item *rmap_item;
> +
> +	rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL);
> +	if (rmap_item)
> +		ksm_rmap_items++;
> +	return rmap_item;
>  }

ksm_rmap_items was already available via /proc/slabinfo.  I guess that
wasn't a particularly nice user interface ;)