* [PATCH] memcg: add support to generate the total count of children from root
@ 2020-11-24 10:58 Aaron Tomlin
2020-11-24 11:26 ` Michal Hocko
0 siblings, 1 reply; 6+ messages in thread
From: Aaron Tomlin @ 2020-11-24 10:58 UTC (permalink / raw)
To: linux-kernel; +Cc: hannes, mhocko, vdavydov.dev, akpm, cgroups, linux-mm
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.
Signed-off-by: Aaron Tomlin <atomlin@redhat.com>
---
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
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH] memcg: add support to generate the total count of children from root
2020-11-24 10:58 [PATCH] memcg: add support to generate the total count of children from root Aaron Tomlin
@ 2020-11-24 11:26 ` Michal Hocko
2020-11-24 13:36 ` Aaron Tomlin
[not found] ` <CANfR36hyrqXjk2tL03GzCk6rn6sCD7Sd811soBsZC3dHY0h9fQ@mail.gmail.com>
0 siblings, 2 replies; 6+ messages in thread
From: Michal Hocko @ 2020-11-24 11:26 UTC (permalink / raw)
To: Aaron Tomlin; +Cc: linux-kernel, hannes, vdavydov.dev, akpm, cgroups, linux-mm
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@redhat.com>
> ---
> 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
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] memcg: add support to generate the total count of children from root
2020-11-24 11:26 ` Michal Hocko
@ 2020-11-24 13:36 ` Aaron Tomlin
[not found] ` <CANfR36hyrqXjk2tL03GzCk6rn6sCD7Sd811soBsZC3dHY0h9fQ@mail.gmail.com>
1 sibling, 0 replies; 6+ messages in thread
From: Aaron Tomlin @ 2020-11-24 13:36 UTC (permalink / raw)
To: Michal Hocko
Cc: linux-kernel, hannes, vdavydov.dev, Andrew Morton, cgroups, linux-mm
On Tue, 24 Nov 2020 at 11:26, Michal Hocko <mhocko@suse.com> wrote:
>
> 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.
>
Hi Michal,
> 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.
Thank you for your feedback.
Indeed, one can use a command/script to manually calculate this.
Having said that, one that creates a significant number of
memory-controlled cgroups may prefer a quick, simple and reliable method
to generate the aforementioned data, for management purposes only.
As such, I thought this patch might be particularly useful.
Kind regards,
--
Aaron Tomlin
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] memcg: add support to generate the total count of children from root
[not found] ` <CANfR36hyrqXjk2tL03GzCk6rn6sCD7Sd811soBsZC3dHY0h9fQ@mail.gmail.com>
@ 2020-11-24 13:36 ` Michal Hocko
2020-11-24 13:47 ` Aaron Tomlin
0 siblings, 1 reply; 6+ messages in thread
From: Michal Hocko @ 2020-11-24 13:36 UTC (permalink / raw)
To: Aaron Tomlin
Cc: linux-kernel, hannes, vdavydov.dev, Andrew Morton, cgroups, linux-mm
On Tue 24-11-20 13:27:32, Aaron Tomlin wrote:
> On Tue, 24 Nov 2020 at 11:26, Michal Hocko <mhocko@suse.com> wrote:
>
> > 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.
> >
>
> Hi Michal,
>
>
> > 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.
> >
>
> Thank you for your feedback.
>
> Indeed, one can use a command/script to manually calculate this.
> Having said that, one that creates a significant number of
> memory-controlled cgroups may prefer a quick, simple and reliable method
> to generate the aforementioned data, for management purposes only.
> As such, I thought this patch might be particularly useful.
This like any other user visible interface would be a much easier sell
if there was a clear usecase to justify it. I do not see anything
controversial about exporting such a value but my general take is that
we are only adding new interface when existing ones are insufficient. A
performance might be a very good reason but that would really require to
come with some real life numbers.
Thanks!
--
Michal Hocko
SUSE Labs
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] memcg: add support to generate the total count of children from root
2020-11-24 13:36 ` Michal Hocko
@ 2020-11-24 13:47 ` Aaron Tomlin
2020-11-26 11:02 ` Aaron Tomlin
0 siblings, 1 reply; 6+ messages in thread
From: Aaron Tomlin @ 2020-11-24 13:47 UTC (permalink / raw)
To: Michal Hocko
Cc: linux-kernel, hannes, vdavydov.dev, Andrew Morton, cgroups, linux-mm
On Tue, 24 Nov 2020 at 13:36, Michal Hocko <mhocko@suse.com> wrote:
Michal,
> This like any other user visible interface would be a much easier sell
> if there was a clear usecase to justify it. I do not see anything
> controversial about exporting such a value but my general take is that
> we are only adding new interface when existing ones are insufficient. A
> performance might be a very good reason but that would really require to
> come with some real life numbers.
Fair enough and understood.
At this stage, I unfortunately do not have such supporting data. This was only
useful in an isolated situation. Having said this, I thought that the
aforementioned interface would be helpful to others, in particular, given the
known limitation.
Kind regards,
--
Aaron Tomlin
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] memcg: add support to generate the total count of children from root
2020-11-24 13:47 ` Aaron Tomlin
@ 2020-11-26 11:02 ` Aaron Tomlin
0 siblings, 0 replies; 6+ messages in thread
From: Aaron Tomlin @ 2020-11-26 11:02 UTC (permalink / raw)
To: Michal Hocko
Cc: linux-kernel, hannes, vdavydov.dev, Andrew Morton, cgroups, linux-mm
On Tue 2020-11-24 13:47 +0000, Aaron Tomlin wrote:
> On Tue, 24 Nov 2020 at 13:36, Michal Hocko <mhocko@suse.com> wrote:
> > This like any other user visible interface would be a much easier sell
> > if there was a clear usecase to justify it. I do not see anything
> > controversial about exporting such a value but my general take is that
> > we are only adding new interface when existing ones are insufficient. A
> > performance might be a very good reason but that would really require to
> > come with some real life numbers.
Michal,
> Fair enough and understood.
>
> At this stage, I unfortunately do not have such supporting data. This was only
> useful in an isolated situation. Having said this, I thought that the
> aforementioned interface would be helpful to others, in particular, given the
> known limitation.
Furthermore, I can see that this is already provided via /proc/cgroups
(see proc_cgroupstats_show()). As such, another possibility:
the proposed interface could reliably produce the difference between the
maximum permitted memory-controlled cgroup count and the used count
(i.e. the remaining memory cgroup count, from root); albeit, I doubt that
this would be particularly useful to others i.e., the use-case would be
rather limited.
Kind regards,
--
Aaron Tomlin
^ permalink raw reply [flat|nested] 6+ messages in thread
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2020-11-24 10:58 [PATCH] memcg: add support to generate the total count of children from root Aaron Tomlin
2020-11-24 11:26 ` Michal Hocko
2020-11-24 13:36 ` Aaron Tomlin
[not found] ` <CANfR36hyrqXjk2tL03GzCk6rn6sCD7Sd811soBsZC3dHY0h9fQ@mail.gmail.com>
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2020-11-26 11:02 ` Aaron Tomlin
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