On Fri 09-01-15 11:09:43, Vladimir Davydov wrote:
> Since commit b2052564e66d ("mm: memcontrol: continue cache reclaim from
> offlined groups") pages charged to a memory cgroup are not reparented
> when the cgroup is removed. Instead, they are supposed to be reclaimed
> in a regular way, along with pages accounted to online memory cgroups.
>
> However, an lruvec of an offline memory cgroup will sooner or later get
> so small that it will be scanned only at low scan priorities (see
> get_scan_count()). Therefore, if there are enough reclaimable pages in
> big lruvecs, pages accounted to offline memory cgroups will never be
> scanned at all, wasting memory.
>
> Fix this by unconditionally forcing scanning dead lruvecs from kswapd.
>
> Signed-off-by: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxx>
Thanks!
> ---
> Changes in v2:
> - code style fixes (Johannes)
>
> include/linux/memcontrol.h | 6 ++++++
> mm/memcontrol.c | 14 ++++++++++++++
> mm/vmscan.c | 8 ++++++--
> 3 files changed, 26 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 76b4084b8d08..68f3b44ef27c 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -102,6 +102,7 @@ void mem_cgroup_iter_break(struct mem_cgroup *, struct mem_cgroup *);
> * For memory reclaim.
> */
> int mem_cgroup_inactive_anon_is_low(struct lruvec *lruvec);
> +bool mem_cgroup_lruvec_online(struct lruvec *lruvec);
> int mem_cgroup_select_victim_node(struct mem_cgroup *memcg);
> unsigned long mem_cgroup_get_lru_size(struct lruvec *lruvec, enum lru_list);
> void mem_cgroup_update_lru_size(struct lruvec *, enum lru_list, int);
> @@ -266,6 +267,11 @@ mem_cgroup_inactive_anon_is_low(struct lruvec *lruvec)
> return 1;
> }
>
> +bool mem_cgroup_lruvec_online(struct lruvec *lruvec)
> +{
> + return true;
> +}
> +
> static inline unsigned long
> mem_cgroup_get_lru_size(struct lruvec *lruvec, enum lru_list lru)
> {
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index bfa1a849d113..67c936bbaa13 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1367,6 +1367,20 @@ int mem_cgroup_inactive_anon_is_low(struct lruvec *lruvec)
> return inactive * inactive_ratio < active;
> }
>
> +bool mem_cgroup_lruvec_online(struct lruvec *lruvec)
> +{
> + struct mem_cgroup_per_zone *mz;
> + struct mem_cgroup *memcg;
> +
> + if (mem_cgroup_disabled())
> + return true;
> +
> + mz = container_of(lruvec, struct mem_cgroup_per_zone, lruvec);
> + memcg = mz->memcg;
> +
> + return !!(memcg->css.flags & CSS_ONLINE);
> +}
> +
> #define mem_cgroup_from_counter(counter, member) \
> container_of(counter, struct mem_cgroup, member)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index e29f411b38ac..38173d9a2a87 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1935,8 +1935,12 @@ static void get_scan_count(struct lruvec *lruvec, int swappiness,
> * latencies, so it's better to scan a minimum amount there as
> * well.
> */
> - if (current_is_kswapd() && !zone_reclaimable(zone))
> - force_scan = true;
> + if (current_is_kswapd()) {
> + if (!zone_reclaimable(zone))
> + force_scan = true;
> + if (!mem_cgroup_lruvec_online(lruvec))
> + force_scan = true;
> + }
> if (!global_reclaim(sc))
> force_scan = true;
>
> --
> 1.7.10.4
>
--
Michal Hocko
SUSE Labs
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