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

Andrew Morton
2012-11-02T00:05:42Z

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, 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;
}