Re: [PATCH v6 11/29] memcg: allow a memcg with kmem charges to be destructed.

Michal Hocko
2012-11-06T10:54:31Z

On Thu 01-11-12 17:05:39, Andrew Morton wrote:
> On Thu, 1 Nov 2012 16:07:27 +0400
> Glauber Costa <glommer@parallels.com> wrote:
>
> > Because the ultimate goal of the kmem tracking in memcg is to track slab
> > pages as well, we can't guarantee that we'll always be able to point a
> > page to a particular process, and migrate the charges along with it -
> > since in the common case, a page will contain data belonging to multiple
> > processes.
> >
> > Because of that, when we destroy a memcg, we only make sure the
> > destruction will succeed by discounting the kmem charges from the user
> > charges when we try to empty the cgroup.
>
> There was a significant conflict with the sched/numa changes in
> linux-next,

Just for record. The conflict was introduced by 2ef37d3f (memcg: Simplify
mem_cgroup_force_empty_list error handling) which came in via Tejun's
tree.
Your resolution looks good to me. Sorry about the trouble.

> which I resolved as below. Please check it.
>
> static int mem_cgroup_reparent_charges(struct mem_cgroup *memcg)
> {
> struct cgroup *cgrp = memcg->css.cgroup;
> int node, zid;
> u64 usage;
>
> do {
> if (cgroup_task_count(cgrp) || !list_empty(&cgrp->children))
> return -EBUSY;
> /* This is for making all *used* pages to be on LRU. */
> lru_add_drain_all();
> drain_all_stock_sync(memcg);
> mem_cgroup_start_move(memcg);
> for_each_node_state(node, N_HIGH_MEMORY) {
> for (zid = 0; zid < MAX_NR_ZONES; zid++) {
> enum lru_list lru;
> for_each_lru(lru) {
> mem_cgroup_force_empty_list(memcg,
> node, zid, lru);
> }
> }
> }
> mem_cgroup_end_move(memcg);
> memcg_oom_recover(memcg);
> cond_resched();
>
> /*
> * Kernel memory may not necessarily be trackable to a specific
> * process. So they are not migrated, and therefore we can't
> * expect their value to drop to 0 here.
> * Having res filled up with kmem only is enough.
> *
> * This is a safety check because mem_cgroup_force_empty_list
> * could have raced with mem_cgroup_replace_page_cache callers
> * so the lru seemed empty but the page could have been added
> * right after the check. RES_USAGE should be safe as we always
> * charge before adding to the LRU.
> */
> usage = res_counter_read_u64(&memcg->res, RES_USAGE) -
> res_counter_read_u64(&memcg->kmem, RES_USAGE);
> } while (usage > 0);
>
> return 0;
> }
>

--
Michal Hocko
SUSE Labs