| From: Chen Yu <yu.c.chen@intel.com> |
| Subject: Revert "sched/numa: add statistics of numa balance task" |
| Date: Fri, 4 Jul 2025 21:56:20 +0800 |
| |
| 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. |
| |
| Link: https://lkml.kernel.org/r/20250704135620.685752-1-yu.c.chen@intel.com |
| Link: https://lkml.kernel.org/r/20250708064917.BBD13C4CEED@smtp.kernel.org |
| Fixes: ad6b26b6a0a7 ("sched/numa: add statistics of numa balance task") |
| Signed-off-by: Chen Yu <yu.c.chen@intel.com> |
| Reported-by: Jirka Hladky <jhladky@redhat.com> |
| Closes: https://lore.kernel.org/all/CAE4VaGBLJxpd=NeRJXpSCuw=REhC5LWJpC29kDy-Zh2ZDyzQZA@mail.gmail.com/ |
| Reported-by: Srikanth Aithal <Srikanth.Aithal@amd.com> |
| Reported-by: Suneeth D <Suneeth.D@amd.com> |
| Acked-by: Michal Hocko <mhocko@suse.com> |
| Cc: Borislav Petkov <bp@alien8.de> |
| Cc: Ingo Molnar <mingo@redhat.com> |
| Cc: Jiri Hladky <jhladky@redhat.com> |
| Cc: Libo Chen <libo.chen@oracle.com> |
| Cc: Peter Zijlstra <peterz@infradead.org> |
| Cc: Thomas Gleixner <tglx@linutronix.de> |
| Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
| --- |
| |
| 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(-) |
| |
| --- a/Documentation/admin-guide/cgroup-v2.rst~revert-sched-numa-add-statistics-of-numa-balance-task |
| +++ a/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. |
| |
| --- a/include/linux/sched.h~revert-sched-numa-add-statistics-of-numa-balance-task |
| +++ a/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; |
| --- a/include/linux/vm_event_item.h~revert-sched-numa-add-statistics-of-numa-balance-task |
| +++ a/include/linux/vm_event_item.h |
| @@ -66,8 +66,6 @@ enum vm_event_item { PGPGIN, PGPGOUT, PS |
| NUMA_HINT_FAULTS, |
| NUMA_HINT_FAULTS_LOCAL, |
| NUMA_PAGE_MIGRATE, |
| - NUMA_TASK_MIGRATE, |
| - NUMA_TASK_SWAP, |
| #endif |
| #ifdef CONFIG_MIGRATION |
| PGMIGRATE_SUCCESS, PGMIGRATE_FAIL, |
| --- a/kernel/sched/core.c~revert-sched-numa-add-statistics-of-numa-balance-task |
| +++ a/kernel/sched/core.c |
| @@ -3362,10 +3362,6 @@ void set_task_cpu(struct task_struct *p, |
| #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; |
| @@ -7939,9 +7935,8 @@ int migrate_task_to(struct task_struct * |
| 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); |
| } |
| --- a/kernel/sched/debug.c~revert-sched-numa-add-statistics-of-numa-balance-task |
| +++ a/kernel/sched/debug.c |
| @@ -1210,10 +1210,6 @@ void proc_sched_show_task(struct task_st |
| 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); |
| --- a/mm/memcontrol.c~revert-sched-numa-add-statistics-of-numa-balance-task |
| +++ a/mm/memcontrol.c |
| @@ -474,8 +474,6 @@ static const unsigned int memcg_vm_event |
| NUMA_PAGE_MIGRATE, |
| NUMA_PTE_UPDATES, |
| NUMA_HINT_FAULTS, |
| - NUMA_TASK_MIGRATE, |
| - NUMA_TASK_SWAP, |
| #endif |
| }; |
| |
| --- a/mm/vmstat.c~revert-sched-numa-add-statistics-of-numa-balance-task |
| +++ a/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", |
| _ |
