On Tue 24-11-20 10:58:36, Aaron Tomlin wrote:
> Each memory-controlled cgroup is assigned a unique ID and the total
> number of memory cgroups is limited to MEM_CGROUP_ID_MAX.
>
> This patch provides the ability to determine the number of
> memory cgroups from the root memory cgroup, only.
> A value of 1 (i.e. self count) is returned if there are no children.
> For example, the number of memory cgroups can be established by
> reading the /sys/fs/cgroup/memory/memory.total_cnt file.
Could you add some explanation why is this information useful for
userspace? Who is going to use it and why a simple scripting on top of
cgroupfs is insufficient.
> Signed-off-by: Aaron Tomlin <atomlin@xxxxxxxxxx>
> ---
> mm/memcontrol.c | 18 ++++++++++++++++++
> 1 file changed, 18 insertions(+)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 29459a6ce1c7..a4f7cb40e233 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -4535,6 +4535,19 @@ static int mem_cgroup_oom_control_write(struct cgroup_subsys_state *css,
> return 0;
> }
>
> +static int mem_cgroup_total_count_read(struct cgroup_subsys_state *css,
> + struct cftype *cft)
> +{
> + struct mem_cgroup *iter, *memcg = mem_cgroup_from_css(css);
> + int num = 0;
> +
> + for_each_mem_cgroup_tree(iter, memcg)
> + num++;
> +
> + /* Returns 1 (i.e. self count) if no children. */
> + return num;
> +}
> +
> #ifdef CONFIG_CGROUP_WRITEBACK
>
> #include <trace/events/writeback.h>
> @@ -5050,6 +5063,11 @@ static struct cftype mem_cgroup_legacy_files[] = {
> .write_u64 = mem_cgroup_oom_control_write,
> .private = MEMFILE_PRIVATE(_OOM_TYPE, OOM_CONTROL),
> },
> + {
> + .name = "total_cnt",
> + .flags = CFTYPE_ONLY_ON_ROOT,
> + .read_u64 = mem_cgroup_total_count_read,
> + },
> {
> .name = "pressure_level",
> },
> --
> 2.26.2
>
--
Michal Hocko
SUSE Labs
