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Message-ID: <8caab4ad-4525-4d11-8512-bf83f607bd76@intel.com>
Date: Tue, 29 Apr 2025 19:18:27 +0800
From: "Chen, Yu C" <yu.c.chen@...el.com>
To: Libo Chen <libo.chen@...cle.com>
CC: <cgroups@...r.kernel.org>, <linux-doc@...r.kernel.org>,
<linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>, Tim Chen
<tim.c.chen@...el.com>, Aubrey Li <aubrey.li@...el.com>, Chen Yu
<yu.chen.surf@...mail.com>, K Prateek Nayak <kprateek.nayak@....com>, "Madadi
Vineeth Reddy" <vineethr@...ux.ibm.com>, Muchun Song <muchun.song@...ux.dev>,
Roman Gushchin <roman.gushchin@...ux.dev>, Michal Hocko <mhocko@...nel.org>,
Mel Gorman <mgorman@...e.de>, Jonathan Corbet <corbet@....net>, "Johannes
Weiner" <hannes@...xchg.org>, Michal Koutny <mkoutny@...e.com>, Tejun Heo
<tj@...nel.org>, Ingo Molnar <mingo@...hat.com>, Shakeel Butt
<shakeel.butt@...ux.dev>, Andrew Morton <akpm@...ux-foundation.org>, "Peter
Zijlstra" <peterz@...radead.org>
Subject: Re: [PATCH v2] sched/numa: Add statistics of numa balance task
migration and swap
Hi Libo,
On 4/29/2025 7:10 AM, Libo Chen wrote:
> Hi Chen Yu,
>
> I think this is quite useful! I hope it can be picked up.
>
> I have one comment below
>
> On 4/8/25 03:14, Chen Yu wrote:
>> On systems with NUMA balancing enabled, it is found that tracking
>> the task activities due to NUMA balancing is helpful. NUMA balancing
>> has two mechanisms for task migration: one is to migrate the task to
>> an idle CPU in its preferred node, the other is to swap tasks on
>> different nodes if they are on each other's preferred node.
>>
>> The kernel already has NUMA page migration statistics in
>> /sys/fs/cgroup/mytest/memory.stat and /proc/{PID}/sched,
>> but does not have statistics for task migration/swap.
>> Add the task migration and swap count accordingly.
>>
>> The following two new fields:
>>
>> numa_task_migrated
>> numa_task_swapped
>>
>> will be displayed in both
>> /sys/fs/cgroup/{GROUP}/memory.stat and /proc/{PID}/sched
>>
>> Introducing both pertask and permemcg NUMA balancing statistics helps
>> to quickly evaluate the performance and resource usage of the target
>> workload. For example, the user can first identify the container which
>> has high NUMA balance activity and then narrow down to a specific task
>> within that group, and tune the memory policy of that task.
>> In summary, it is plausible to iterate the /proc/$pid/sched to find the
>> offending task, but the introduction of per memcg tasks' Numa balancing
>> aggregated activity can further help users identify the task in a
>> divide-and-conquer way.
>>
>> Tested-by: K Prateek Nayak <kprateek.nayak@....com>
>> Tested-by: Madadi Vineeth Reddy <vineethr@...ux.ibm.com>
>> Signed-off-by: Chen Yu <yu.c.chen@...el.com>
>> ---
>> v1->v2:
>> Update the Documentation/admin-guide/cgroup-v2.rst. (Michal)
>> ---
>> Documentation/admin-guide/cgroup-v2.rst | 6 ++++++
>> include/linux/sched.h | 4 ++++
>> include/linux/vm_event_item.h | 2 ++
>> kernel/sched/core.c | 10 ++++++++--
>> kernel/sched/debug.c | 4 ++++
>> mm/memcontrol.c | 2 ++
>> mm/vmstat.c | 2 ++
>> 7 files changed, 28 insertions(+), 2 deletions(-)
>>
>> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
>> index f293a13b42ed..b698be14942c 100644
>> --- a/Documentation/admin-guide/cgroup-v2.rst
>> +++ b/Documentation/admin-guide/cgroup-v2.rst
>> @@ -1652,6 +1652,12 @@ The following nested keys are defined.
>> numa_hint_faults (npn)
>> Number of NUMA hinting faults.
>>
>> + numa_task_migrated (npn)
>> + Number of task migration by NUMA balancing.
>> +
>> + numa_task_swapped (npn)
>> + Number of task swap by NUMA balancing.
>> +
>> pgdemote_kswapd
>> Number of pages demoted by kswapd.
>>
>> diff --git a/include/linux/sched.h b/include/linux/sched.h
>> index 56ddeb37b5cd..2e91326c16ec 100644
>> --- a/include/linux/sched.h
>> +++ b/include/linux/sched.h
>> @@ -549,6 +549,10 @@ struct sched_statistics {
>> u64 nr_failed_migrations_running;
>> u64 nr_failed_migrations_hot;
>> u64 nr_forced_migrations;
>> +#ifdef CONFIG_NUMA_BALANCING
>> + u64 numa_task_migrated;
>> + u64 numa_task_swapped;
>> +#endif
>>
>> u64 nr_wakeups;
>> u64 nr_wakeups_sync;
>> diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
>> index 5a37cb2b6f93..df8a1b30930f 100644
>> --- a/include/linux/vm_event_item.h
>> +++ b/include/linux/vm_event_item.h
>> @@ -64,6 +64,8 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
>> NUMA_HINT_FAULTS,
>> NUMA_HINT_FAULTS_LOCAL,
>> NUMA_PAGE_MIGRATE,
>> + NUMA_TASK_MIGRATE,
>> + NUMA_TASK_SWAP,
>> #endif
>> #ifdef CONFIG_MIGRATION
>> PGMIGRATE_SUCCESS, PGMIGRATE_FAIL,
>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> index b434c2f7e3c1..54e7d63f7785 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>> @@ -3352,6 +3352,11 @@ void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
>> #ifdef CONFIG_NUMA_BALANCING
>> static void __migrate_swap_task(struct task_struct *p, int cpu)
>> {
>> + __schedstat_inc(p->stats.numa_task_swapped);
>> +
>> + if (p->mm)
>> + count_memcg_events_mm(p->mm, NUMA_TASK_SWAP, 1);
>> +
>
> Is p->mm check necessary? I am pretty sure a !p->mm task cannot reach to this point,
> task_tick_numa() will filter out those tasks, no hinting page fault on such ones.
Right, kernel thread is not supposed to reach here.
The swap task is obtained from env->best_task, which is assigned by the
functions task_numa_compare() and task_numa_assign(), iff that task has
a valid numa_preferred_nid . In other words, only when the swap task is
a non-kernel thread will it possess a valid numa_preferred_nid.
Let me remove these checks both in __migrate_swap_task and
migrate_task_to().
Thanks,
Chenyu
> We can add a likely() macro here to minimize the overhead if there is a reason to
> keep that check.
>
> Same comment to the other one in migrate_task_to().
>
>
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