Re: SLUB: The unqueued Slab allocator

Peter Zijlstra
2007-02-22T08:40:00Z

On Wed, 2007-02-21 at 23:00 -0800, Christoph Lameter wrote:

> +/*
> + * Lock order:
> + * 1. slab_lock(page)
> + * 2. slab->list_lock
> + *

That seems to contradict this:

> +/*
> + * Lock page and remove it from the partial list
> + *
> + * Must hold list_lock
> + */
> +static __always_inline int lock_and_del_slab(struct kmem_cache *s,
> + struct page *page)
> +{
> + if (slab_trylock(page)) {
> + list_del(&page->lru);
> + s->nr_partial--;
> + return 1;
> + }
> + return 0;
> +}
> +
> +/*
> + * Get a partial page, lock it and return it.
> + */
> +#ifdef CONFIG_NUMA
> +static struct page *get_partial(struct kmem_cache *s, gfp_t flags, int node)
> +{
> + struct page *page;
> + int searchnode = (node == -1) ? numa_node_id() : node;
> +
> + if (!s->nr_partial)
> + return NULL;
> +
> + spin_lock(&s->list_lock);
> + /*
> + * Search for slab on the right node
> + */
> + list_for_each_entry(page, &s->partial, lru)
> + if (likely(page_to_nid(page) == searchnode) &&
> + lock_and_del_slab(s, page))
> + goto out;
> +
> + if (likely(!(flags & __GFP_THISNODE))) {
> + /*
> + * We can fall back to any other node in order to
> + * reduce the size of the partial list.
> + */
> + list_for_each_entry(page, &s->partial, lru)
> + if (likely(lock_and_del_slab(s, page)))
> + goto out;
> + }
> +
> + /* Nothing found */
> + page = NULL;
> +out:
> + spin_unlock(&s->list_lock);
> + return page;
> +}
> +#else
> +static struct page *get_partial(struct kmem_cache *s, gfp_t flags, int node)
> +{
> + struct page *page;
> +
> + /*
> + * Racy check. If we mistakenly see no partial slabs then we
> + * just allocate an empty slab.
> + */
> + if (!s->nr_partial)
> + return NULL;
> +
> + spin_lock(&s->list_lock);
> + list_for_each_entry(page, &s->partial, lru)
> + if (likely(lock_and_del_slab(s, page)))
> + goto out;
> +
> + /* No slab or all slabs busy */
> + page = NULL;
> +out:
> + spin_unlock(&s->list_lock);
> + return page;
> +}
> +#endif