On Thu,  1 Nov 2012 16:07:27 +0400
Glauber Costa [off-list ref] 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, 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;
}

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>