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SubjectRe: [PATCH] slab: Fix kmem_cache_destroy() on NUMA
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.

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