shrink_slab
unsigned long shrink_slab(gfp_t gfp_mask, int nid, struct mem_cgroup *memcg,
freed += shrink_slab(GFP_KERNEL, nid, memcg, 0);
shrink_slab(sc->gfp_mask, pgdat->node_id, memcg, sc->priority);
shrink_slab(sc->gfp_mask, pgdat->node_id, memcg,