On 06/26/2012 09:59 AM, Kamezawa Hiroyuki wrote:
> (2012/06/25 23:15), Glauber Costa 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.
>>
>> Signed-off-by: Glauber Costa <glommer@xxxxxxxxxxxxx>
>> CC: Christoph Lameter <cl@xxxxxxxxx>
>> CC: Pekka Enberg <penberg@xxxxxxxxxxxxxx>
>> CC: Michal Hocko <mhocko@xxxxxxx>
>> CC: Kamezawa Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
>> CC: Johannes Weiner <hannes@xxxxxxxxxxx>
>> CC: Suleiman Souhlal <suleiman@xxxxxxxxxx>
>> ---
>> mm/memcontrol.c | 10 +++++++++-
>> 1 file changed, 9 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index a6a440b..bb9b6fe 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -598,6 +598,11 @@ static void disarm_kmem_keys(struct mem_cgroup *memcg)
>> {
>> if (test_bit(KMEM_ACCOUNTED_THIS, &memcg->kmem_accounted))
>> static_key_slow_dec(&mem_cgroup_kmem_enabled_key);
>> + /*
>> + * This check can't live in kmem destruction function,
>> + * since the charges will outlive the cgroup
>> + */
>> + BUG_ON(res_counter_read_u64(&memcg->kmem, RES_USAGE) != 0);
>> }
>> #else
>> static void disarm_kmem_keys(struct mem_cgroup *memcg)
>> @@ -3838,6 +3843,7 @@ static int mem_cgroup_force_empty(struct mem_cgroup *memcg, bool free_all)
>> int node, zid, shrink;
>> int nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
>> struct cgroup *cgrp = memcg->css.cgroup;
>> + u64 usage;
>>
>> css_get(&memcg->css);
>>
>> @@ -3877,8 +3883,10 @@ move_account:
>> if (ret == -ENOMEM)
>> goto try_to_free;
>> cond_resched();
>> + usage = res_counter_read_u64(&memcg->res, RES_USAGE) -
>> + res_counter_read_u64(&memcg->kmem, RES_USAGE);
>> /* "ret" should also be checked to ensure all lists are empty. */
>> - } while (res_counter_read_u64(&memcg->res, RES_USAGE) > 0 || ret);
>> + } while (usage > 0 || ret);
>> out:
>> css_put(&memcg->css);
>> return ret;
>>
> Hm....maybe work enough. Could you add more comments on the code ?
>
> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
>
I always can.
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