Re: [PATCH] slab: Fix kmem_cache_destroy() on NUMA

[Or Gerlitz <ogerlitz@voltaire.com>]

Roland Dreier wrote:
> With CONFIG_NUMA set, kmem_cache_destroy() may fail and say "Can't
> free all objects."  The problem is caused by sequences such as the
> following (suppose we are on a NUMA machine with two nodes, 0 and 1):
> 
>  * Allocate an object from cache on node 0.
>  * Free the object on node 1.  The object is put into node 1's alien
>    array_cache for node 0.
>  * Call kmem_cache_destroy(), which ultimately ends up in __cache_shrink().
>  * __cache_shrink() does drain_cpu_caches(), which loops through all nodes.
>    For each node it drains the shared array_cache and then handles the
>    alien array_cache for the other node.
> 
> However this means that node 0's shared array_cache will be drained,
> and then node 1 will move the contents of its alien[0] array_cache
> into that same shared array_cache.  node 0's shared array_cache is
> never looked at again, so the objects left there will appear to be in
> use when __cache_shrink() calls __node_shrink() for node 0.  So
> __node_shrink() will return 1 and kmem_cache_destroy() will fail.
> 
> This patch fixes this by having drain_cpu_caches() do
> drain_alien_cache() on every node before it does drain_array() on the
> nodes' shared array_caches.
> 
> The problem was originally reported by Or Gerlitz <ogerlitz@voltaire.com>.
> 
> Cc: Christoph Lameter <clameter@sgi.com>
> Cc: Pekka Enberg <penberg@cs.helsinki.fi>

OK, Indeed i have CONFIG_NUMA and yes, the patch fixes my problem, 
thanks a lot for working on that!

Or.