On Fri, Jan 4, 2019 at 4:21 PM Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx> wrote:
>
> We have some usecases which create and remove memcgs very frequently,
> and the tasks in the memcg may just access the files which are unlikely
> accessed by anyone else. So, we prefer force_empty the memcg before
> rmdir'ing it to reclaim the page cache so that they don't get
> accumulated to incur unnecessary memory pressure. Since the memory
> pressure may incur direct reclaim to harm some latency sensitive
> applications.
>
> Force empty would help out such usecase, however force empty reclaims
> memory synchronously when writing to memory.force_empty. It may take
> some time to return and the afterwards operations are blocked by it.
> Although this can be done in background, some usecases may need create
> new memcg with the same name right after the old one is deleted. So,
> the creation might get blocked by the before reclaim/remove operation.
>
> Delaying memory reclaim in cgroup offline for such usecase sounds
> reasonable. Introduced a new interface, called wipe_on_offline for both
> default and legacy hierarchy, which does memory reclaim in css offline
> kworker.
>
> Writing to 1 would enable it, writing 0 would disable it.
>
> Suggested-by: Michal Hocko <mhocko@xxxxxxxx>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Signed-off-by: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
> ---
> include/linux/memcontrol.h | 3 +++
> mm/memcontrol.c | 49 ++++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 52 insertions(+)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 83ae11c..2f1258a 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -311,6 +311,9 @@ struct mem_cgroup {
> struct list_head event_list;
> spinlock_t event_list_lock;
>
> + /* Reclaim as much as possible memory in offline kworker */
> + bool wipe_on_offline;
> +
> struct mem_cgroup_per_node *nodeinfo[0];
> /* WARNING: nodeinfo must be the last member here */
> };
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 75208a2..5a13c6b 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2918,6 +2918,35 @@ static ssize_t mem_cgroup_force_empty_write(struct kernfs_open_file *of,
> return mem_cgroup_force_empty(memcg) ?: nbytes;
> }
>
> +static int wipe_on_offline_show(struct seq_file *m, void *v)
> +{
> + struct mem_cgroup *memcg = mem_cgroup_from_css(seq_css(m));
> +
> + seq_printf(m, "%lu\n", (unsigned long)memcg->wipe_on_offline);
> +
> + return 0;
> +}
> +
> +static int wipe_on_offline_write(struct cgroup_subsys_state *css,
> + struct cftype *cft, u64 val)
> +{
> + int ret = 0;
> +
> + struct mem_cgroup *memcg = mem_cgroup_from_css(css);
> +
> + if (mem_cgroup_is_root(memcg))
> + return -EINVAL;
> +
> + if (val == 0)
> + memcg->wipe_on_offline = false;
> + else if (val == 1)
> + memcg->wipe_on_offline = true;
> + else
> + ret = -EINVAL;
> +
> + return ret;
> +}
> +
> static u64 mem_cgroup_hierarchy_read(struct cgroup_subsys_state *css,
> struct cftype *cft)
> {
> @@ -4283,6 +4312,11 @@ static ssize_t memcg_write_event_control(struct kernfs_open_file *of,
> .write = mem_cgroup_reset,
> .read_u64 = mem_cgroup_read_u64,
> },
> + {
> + .name = "wipe_on_offline",
What about "force_empty_on_offline"?
> + .seq_show = wipe_on_offline_show,
> + .write_u64 = wipe_on_offline_write,
> + },
> { }, /* terminate */
> };
>
> @@ -4569,6 +4603,15 @@ static void mem_cgroup_css_offline(struct cgroup_subsys_state *css)
> page_counter_set_min(&memcg->memory, 0);
> page_counter_set_low(&memcg->memory, 0);
>
> + /*
> + * Reclaim as much as possible memory when offlining.
> + *
> + * Do it after min/low is reset otherwise some memory might
> + * be protected by min/low.
> + */
> + if (memcg->wipe_on_offline)
> + mem_cgroup_force_empty(memcg);
> +
mem_cgroup_force_empty() also does drain_all_stock(), so, move
drain_all_stock() in mem_cgroup_css_offline() to the else of 'if
(memcg->wipe_on_offline)'.
> memcg_offline_kmem(memcg);
> wb_memcg_offline(memcg);
>
> @@ -5694,6 +5737,12 @@ static ssize_t memory_oom_group_write(struct kernfs_open_file *of,
> .seq_show = memory_oom_group_show,
> .write = memory_oom_group_write,
> },
> + {
> + .name = "wipe_on_offline",
> + .flags = CFTYPE_NOT_ON_ROOT,
> + .seq_show = wipe_on_offline_show,
> + .write_u64 = wipe_on_offline_write,
> + },
> { } /* terminate */
> };
>
> --
> 1.8.3.1
>
