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[109.81.17.167]) by smtp.gmail.com with UTF8SMTPSA id 5b1f17b1804b1-454a9be5bbfsm55754055e9.34.2025.07.04.07.08.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 04 Jul 2025 07:08:20 -0700 (PDT) Date: Fri, 4 Jul 2025 16:08:18 +0200 From: Michal Hocko To: Chen Yu Cc: Ingo Molnar , Andrew Morton , Peter Zijlstra , Jirka Hladky , Srikanth Aithal , Suneeth D , Libo Chen , linux-kernel@vger.kernel.org Subject: Re: [PATCH] Revert "sched/numa: add statistics of numa balance task" Message-ID: References: <20250704135620.685752-1-yu.c.chen@intel.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250704135620.685752-1-yu.c.chen@intel.com> On Fri 04-07-25 21:56:20, Chen Yu wrote: > This reverts commit ad6b26b6a0a79166b53209df2ca1cf8636296382. > > This commit introduces per-memcg/task NUMA balance statistics, > but unfortunately it introduced a NULL pointer exception due > to the following race condition: After a swap task candidate > was chosen, its mm_struct pointer was set to NULL due to task > exit. Later, when performing the actual task swapping, the > p->mm caused the problem. > > CPU0 CPU1 > : > ... > task_numa_migrate > task_numa_find_cpu > task_numa_compare > # a normal task p is chosen > env->best_task = p > > # p exit: > exit_signals(p); > p->flags |= PF_EXITING > exit_mm > p->mm = NULL; > > migrate_swap_stop > __migrate_swap_task((arg->src_task, arg->dst_cpu) > count_memcg_event_mm(p->mm, NUMA_TASK_SWAP)# p->mm is NULL > > task_lock() should be held and the PF_EXITING flag needs to > be checked to prevent this from happening. After discussion, > the conclusion was that adding a lock is not worthwhile for > some statistics calculations. Revert the change and rely on > the tracepoint for this purpose. > > Fixes: ad6b26b6a0a7 ("sched/numa: add statistics of numa balance task") > Reported-by: Jirka Hladky > Closes: https://lore.kernel.org/all/CAE4VaGBLJxpd=NeRJXpSCuw=REhC5LWJpC29kDy-Zh2ZDyzQZA@mail.gmail.com/ > Reported-by: Srikanth Aithal > Reported-by: Suneeth D > Signed-off-by: Chen Yu Acked-by: Michal Hocko Thanks! > --- > Documentation/admin-guide/cgroup-v2.rst | 6 ------ > include/linux/sched.h | 4 ---- > include/linux/vm_event_item.h | 2 -- > kernel/sched/core.c | 9 ++------- > kernel/sched/debug.c | 4 ---- > mm/memcontrol.c | 2 -- > mm/vmstat.c | 2 -- > 7 files changed, 2 insertions(+), 27 deletions(-) > > diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst > index 0cc35a14afbe..bd98ea3175ec 100644 > --- a/Documentation/admin-guide/cgroup-v2.rst > +++ b/Documentation/admin-guide/cgroup-v2.rst > @@ -1732,12 +1732,6 @@ 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 4f78a64beb52..aa9c5be7a632 100644 > --- a/include/linux/sched.h > +++ b/include/linux/sched.h > @@ -548,10 +548,6 @@ 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 91a3ce9a2687..9e15a088ba38 100644 > --- a/include/linux/vm_event_item.h > +++ b/include/linux/vm_event_item.h > @@ -66,8 +66,6 @@ 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 8988d38d46a3..ca0be74e865b 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -3362,10 +3362,6 @@ 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); > - count_vm_numa_event(NUMA_TASK_SWAP); > - count_memcg_event_mm(p->mm, NUMA_TASK_SWAP); > - > if (task_on_rq_queued(p)) { > struct rq *src_rq, *dst_rq; > struct rq_flags srf, drf; > @@ -7934,9 +7930,8 @@ int migrate_task_to(struct task_struct *p, int target_cpu) > if (!cpumask_test_cpu(target_cpu, p->cpus_ptr)) > return -EINVAL; > > - __schedstat_inc(p->stats.numa_task_migrated); > - count_vm_numa_event(NUMA_TASK_MIGRATE); > - count_memcg_event_mm(p->mm, NUMA_TASK_MIGRATE); > + /* TODO: This is not properly updating schedstats */ > + > trace_sched_move_numa(p, curr_cpu, target_cpu); > return stop_one_cpu(curr_cpu, migration_cpu_stop, &arg); > } > diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c > index 9d71baf08075..557246880a7e 100644 > --- a/kernel/sched/debug.c > +++ b/kernel/sched/debug.c > @@ -1210,10 +1210,6 @@ void proc_sched_show_task(struct task_struct *p, struct pid_namespace *ns, > P_SCHEDSTAT(nr_failed_migrations_running); > P_SCHEDSTAT(nr_failed_migrations_hot); > P_SCHEDSTAT(nr_forced_migrations); > -#ifdef CONFIG_NUMA_BALANCING > - P_SCHEDSTAT(numa_task_migrated); > - P_SCHEDSTAT(numa_task_swapped); > -#endif > P_SCHEDSTAT(nr_wakeups); > P_SCHEDSTAT(nr_wakeups_sync); > P_SCHEDSTAT(nr_wakeups_migrate); > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 902da8a9c643..70fdeda1120b 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -474,8 +474,6 @@ static const unsigned int memcg_vm_event_stat[] = { > NUMA_PAGE_MIGRATE, > NUMA_PTE_UPDATES, > NUMA_HINT_FAULTS, > - NUMA_TASK_MIGRATE, > - NUMA_TASK_SWAP, > #endif > }; > > diff --git a/mm/vmstat.c b/mm/vmstat.c > index 429ae5339bfe..a78d70ddeacd 100644 > --- a/mm/vmstat.c > +++ b/mm/vmstat.c > @@ -1346,8 +1346,6 @@ const char * const vmstat_text[] = { > "numa_hint_faults", > "numa_hint_faults_local", > "numa_pages_migrated", > - "numa_task_migrated", > - "numa_task_swapped", > #endif > #ifdef CONFIG_MIGRATION > "pgmigrate_success", > -- > 2.25.1 > -- Michal Hocko SUSE Labs