On 09/21/2012 08:48 AM, JoonSoo Kim wrote: > Hi Glauber. > Hi > 2012/9/18 Glauber Costa <glommer@xxxxxxxxxxxxx>: >> diff --git a/mm/slub.c b/mm/slub.c >> index 0b68d15..9d79216 100644 >> --- a/mm/slub.c >> +++ b/mm/slub.c >> @@ -2602,6 +2602,7 @@ redo: >> } else >> __slab_free(s, page, x, addr); >> >> + kmem_cache_verify_dead(s); >> } > > As far as u know, I am not a expert and don't know anything about memcg. > IMHO, this implementation may hurt system performance in some case. > > In case of memcg is destoried, remained kmem_cache is marked "dead". > After it is marked, > every free operation to this "dead" kmem_cache call > kmem_cache_verify_dead() and finally call kmem_cache_shrink(). As long as it is restricted to that cache, this is a non issue. dead caches are exactly what they name imply: dead. Means that we actively want them to go away, and just don't kill them right away because they have some inflight objects - which we expect not to be too much. > kmem_cache_shrink() do invoking kmalloc and flush_all() and taking a > lock for online node and invoking kfree. > Especially, flush_all() may hurt performance largely, because it call > has_cpu_slab() against all the cpus. Again, this is all right, but being a dead cache, it shouldn't be on any hot path. > > And, I found one case that destroying memcg's kmem_cache don't works properly. > If we destroy memcg after all object is freed, current implementation > doesn't destroy kmem_cache. > kmem_cache_destroy_work_func() check "cachep->memcg_params.nr_pages == 0", > but in this case, it return false, because kmem_cache may have > cpu_slab, and cpu_partials_slabs. > As we already free all objects, kmem_cache_verify_dead() is not invoked forever. > I think that we need another kmem_cache_shrink() in > kmem_cache_destroy_work_func(). I'll take a look here. What you describe makes sense, and can potentially happen. I tried to handle this case with care in destroy_all_caches, but I may have always made a mistake... Did you see this actively happening, or are you just assuming this can happen from your read of the code? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>