Re: [PATCH] slub: fix off by one in number of slab tests

Vladimir Davydov
2014-06-24T08:16:24Z

On Tue, Jun 24, 2014 at 04:44:01PM +0900, Joonsoo Kim wrote:
> min_partial means minimum number of slab cached in node partial
> list. So, if nr_partial is less than it, we keep newly empty slab
> on node partial list rather than freeing it. But if nr_partial is
> equal or greater than it, it means that we have enough partial slabs
> so should free newly empty slab. Current implementation missed
> the equal case so if we set min_partial is 0, then, at least one slab
> could be cached. This is critical problem to kmemcg destroying logic
> because it doesn't works properly if some slabs is cached. This patch
> fixes this problem.

Oops, my fault :-(

Thank you for catching this!

> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>

Acked-by: Vladimir Davydov <vdavydov@parallels.com>

>
> diff --git a/mm/slub.c b/mm/slub.c
> index c567927..67da14d 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -1851,7 +1851,7 @@ redo:
>
> new.frozen = 0;
>
> - if (!new.inuse && n->nr_partial > s->min_partial)
> + if (!new.inuse && n->nr_partial >= s->min_partial)
> m = M_FREE;
> else if (new.freelist) {
> m = M_PARTIAL;
> @@ -1962,7 +1962,7 @@ static void unfreeze_partials(struct kmem_cache *s,
> new.freelist, new.counters,
> "unfreezing slab"));
>
> - if (unlikely(!new.inuse && n->nr_partial > s->min_partial)) {
> + if (unlikely(!new.inuse && n->nr_partial >= s->min_partial)) {
> page->next = discard_page;
> discard_page = page;
> } else {
> @@ -2595,7 +2595,7 @@ static void __slab_free(struct kmem_cache *s, struct page *page,
> return;
> }
>
> - if (unlikely(!new.inuse && n->nr_partial > s->min_partial))
> + if (unlikely(!new.inuse && n->nr_partial >= s->min_partial))
> goto slab_empty;
>
> /*
> --
> 1.7.9.5
>