On Mon 27-05-19 10:46:43, Shakeel Butt wrote:
> The memory controller in cgroup v2 exposes memory.events file for each
> memcg which shows the number of times events like low, high, max, oom
> and oom_kill have happened for the whole tree rooted at that memcg.
> Users can also poll or register notification to monitor the changes in
> that file. Any event at any level of the tree rooted at memcg will
> notify all the listeners along the path till root_mem_cgroup. There are
> existing users which depend on this behavior.
>
> However there are users which are only interested in the events
> happening at a specific level of the memcg tree and not in the events in
> the underlying tree rooted at that memcg. One such use-case is a
> centralized resource monitor which can dynamically adjust the limits of
> the jobs running on a system. The jobs can create their sub-hierarchy
> for their own sub-tasks. The centralized monitor is only interested in
> the events at the top level memcgs of the jobs as it can then act and
> adjust the limits of the jobs. Using the current memory.events for such
> centralized monitor is very inconvenient. The monitor will keep
> receiving events which it is not interested and to find if the received
> event is interesting, it has to read memory.event files of the next
> level and compare it with the top level one. So, let's introduce
> memory.events.local to the memcg which shows and notify for the events
> at the memcg level.
>
> Now, does memory.stat and memory.pressure need their local versions.
> IMHO no due to the no internal process contraint of the cgroup v2. The
> memory.stat file of the top level memcg of a job shows the stats and
> vmevents of the whole tree. The local stats or vmevents of the top level
> memcg will only change if there is a process running in that memcg but
> v2 does not allow that. Similarly for memory.pressure there will not be
> any process in the internal nodes and thus no chance of local pressure.
>
> Signed-off-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
> Reviewed-by: Roman Gushchin <guro@xxxxxx>
> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
As there seems to be a larger agreement that the default behavior of
memory.events is going to be hierarchical then this addition makes a lot
of sense.
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
> Changelog since v2:
> - Added documentation.
>
> Changelog since v1:
> - refactor memory_events_show to share between events and events.local
>
> Documentation/admin-guide/cgroup-v2.rst | 10 ++++++++
> include/linux/memcontrol.h | 7 ++++-
> mm/memcontrol.c | 34 +++++++++++++++++--------
> 3 files changed, 40 insertions(+), 11 deletions(-)
>
> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
> index 19c4e78666ff..0e961fc90cd9 100644
> --- a/Documentation/admin-guide/cgroup-v2.rst
> +++ b/Documentation/admin-guide/cgroup-v2.rst
> @@ -1119,6 +1119,11 @@ PAGE_SIZE multiple when read back.
> otherwise, a value change in this file generates a file
> modified event.
>
> + Note that all fields in this file are hierarchical and the
> + file modified event can be generated due to an event down the
> + hierarchy. For for the local events at the cgroup level see
> + memory.events.local.
> +
> low
> The number of times the cgroup is reclaimed due to
> high memory pressure even though its usage is under
> @@ -1158,6 +1163,11 @@ PAGE_SIZE multiple when read back.
> The number of processes belonging to this cgroup
> killed by any kind of OOM killer.
>
> + memory.events.local
> + Similar to memory.events but the fields in the file are local
> + to the cgroup i.e. not hierarchical. The file modified event
> + generated on this file reflects only the local events.
> +
> memory.stat
> A read-only flat-keyed file which exists on non-root cgroups.
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 36bdfe8e5965..de77405eec46 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -239,8 +239,9 @@ struct mem_cgroup {
> /* OOM-Killer disable */
> int oom_kill_disable;
>
> - /* memory.events */
> + /* memory.events and memory.events.local */
> struct cgroup_file events_file;
> + struct cgroup_file events_local_file;
>
> /* handle for "memory.swap.events" */
> struct cgroup_file swap_events_file;
> @@ -286,6 +287,7 @@ struct mem_cgroup {
> atomic_long_t vmevents_local[NR_VM_EVENT_ITEMS];
>
> atomic_long_t memory_events[MEMCG_NR_MEMORY_EVENTS];
> + atomic_long_t memory_events_local[MEMCG_NR_MEMORY_EVENTS];
>
> unsigned long socket_pressure;
>
> @@ -761,6 +763,9 @@ static inline void count_memcg_event_mm(struct mm_struct *mm,
> static inline void memcg_memory_event(struct mem_cgroup *memcg,
> enum memcg_memory_event event)
> {
> + atomic_long_inc(&memcg->memory_events_local[event]);
> + cgroup_file_notify(&memcg->events_local_file);
> +
> do {
> atomic_long_inc(&memcg->memory_events[event]);
> cgroup_file_notify(&memcg->events_file);
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 2713b45ec3f0..a57dfcc4c4a4 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -5630,21 +5630,29 @@ static ssize_t memory_max_write(struct kernfs_open_file *of,
> return nbytes;
> }
>
> +static void __memory_events_show(struct seq_file *m, atomic_long_t *events)
> +{
> + seq_printf(m, "low %lu\n", atomic_long_read(&events[MEMCG_LOW]));
> + seq_printf(m, "high %lu\n", atomic_long_read(&events[MEMCG_HIGH]));
> + seq_printf(m, "max %lu\n", atomic_long_read(&events[MEMCG_MAX]));
> + seq_printf(m, "oom %lu\n", atomic_long_read(&events[MEMCG_OOM]));
> + seq_printf(m, "oom_kill %lu\n",
> + atomic_long_read(&events[MEMCG_OOM_KILL]));
> +}
> +
> static int memory_events_show(struct seq_file *m, void *v)
> {
> struct mem_cgroup *memcg = mem_cgroup_from_seq(m);
>
> - seq_printf(m, "low %lu\n",
> - atomic_long_read(&memcg->memory_events[MEMCG_LOW]));
> - seq_printf(m, "high %lu\n",
> - atomic_long_read(&memcg->memory_events[MEMCG_HIGH]));
> - seq_printf(m, "max %lu\n",
> - atomic_long_read(&memcg->memory_events[MEMCG_MAX]));
> - seq_printf(m, "oom %lu\n",
> - atomic_long_read(&memcg->memory_events[MEMCG_OOM]));
> - seq_printf(m, "oom_kill %lu\n",
> - atomic_long_read(&memcg->memory_events[MEMCG_OOM_KILL]));
> + __memory_events_show(m, memcg->memory_events);
> + return 0;
> +}
> +
> +static int memory_events_local_show(struct seq_file *m, void *v)
> +{
> + struct mem_cgroup *memcg = mem_cgroup_from_seq(m);
>
> + __memory_events_show(m, memcg->memory_events_local);
> return 0;
> }
>
> @@ -5806,6 +5814,12 @@ static struct cftype memory_files[] = {
> .file_offset = offsetof(struct mem_cgroup, events_file),
> .seq_show = memory_events_show,
> },
> + {
> + .name = "events.local",
> + .flags = CFTYPE_NOT_ON_ROOT,
> + .file_offset = offsetof(struct mem_cgroup, events_local_file),
> + .seq_show = memory_events_local_show,
> + },
> {
> .name = "stat",
> .flags = CFTYPE_NOT_ON_ROOT,
> --
> 2.22.0.rc1.257.g3120a18244-goog
--
Michal Hocko
SUSE Labs
