On Wed, 29 Oct 2025 21:22:55 +0800 Jiayuan Chen <[email protected]> wrote:
> From: Jiayuan Chen <[email protected]> > > In systems with multiple NUMA nodes, memory imbalance between nodes often > occurs. To address this, we typically tune parameters like scan_size_mb or > scan_period_{min,max}_ms to allow processes to migrate pages between NUMA > nodes. > > Currently, the migration task task_numa_work() holds the mmap_lock during > the entire migration process, which can significantly impact process > performance, especially for memory operations. This patch introduces a new > tracepoint that records the migration duration, along with the number of > scanned pages and migrated pages. These metrics can be used to calculate > efficiency metrics similar to %vmeff in 'sar -B'. > > These metrics help evaluate whether the adjusted NUMA balancing parameters > are properly tuned. > > Here's an example bpftrace script: > ```bash > > bpftrace -e ' > tracepoint:sched:sched_numa_balance_start > { > @start_time[cpu] = nsecs; > } > > tracepoint:sched:sched_numa_balance_end { > if (@start_time[cpu] > 0) { > $cost = nsecs - @start_time[cpu]; > printf("task '%s' migrate cost %lu, scanned %lu, migrated %lu\n", > args.comm, $cost, args.scanned, args.migrated); > } > } > ' BTW, you don't need bpf for this either: # trace-cmd sqlhist -e -n numa_balance SELECT end.comm, TIMESTAMP_DELTA_USECS as cost, \ end.scanned, end.migrated FROM sched_numa_balance_start AS start \ JOIN sched_numa_balance_end AS end ON start.common_pid = end.common_pid # trace-cmd start -e numa_balance [ I'd show the output, but my test boxes don't have NUMA ] You could also make a histogram with it: # trace-cmd sqlhist -e SELECT start.comm, 'CAST(start.cost AS BUCKETS=50)' FROM numa_balance AS start And then cat /sys/kernel/tracing/events/synthetic/numa_balance/hist Just to give you an idea. > ``` > Sample output: > Attaching 2 probes... > task 'rs:main Q:Reg' migrate cost 5584655, scanned 24516, migrated 22373 > task 'systemd-journal' migrate cost 123191, scanned 6308, migrated 0 > task 'wrk' migrate cost 894026, scanned 5842, migrated 5841 > > Signed-off-by: Jiayuan Chen <[email protected]> > --- > include/trace/events/sched.h | 60 ++++++++++++++++++++++++++++++++++++ > kernel/sched/fair.c | 14 +++++++-- > 2 files changed, 72 insertions(+), 2 deletions(-) > > diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h > index 7b2645b50e78..e24bf700a614 100644 > --- a/include/trace/events/sched.h > +++ b/include/trace/events/sched.h > @@ -804,6 +804,66 @@ TRACE_EVENT(sched_skip_cpuset_numa, > __entry->ngid, > MAX_NUMNODES, __entry->mem_allowed) > ); > + > +TRACE_EVENT(sched_numa_balance_start, > + > + TP_PROTO(struct task_struct *tsk), > + > + TP_ARGS(tsk), > + > + TP_STRUCT__entry( > + __array(char, comm, TASK_COMM_LEN) Please use __string() and not __array(). I'm trying to get rid of these for task comm. > + __field(pid_t, pid) > + __field(pid_t, tgid) > + __field(pid_t, ngid) > + ), > + > + TP_fast_assign( > + memcpy(__entry->comm, tsk->comm, TASK_COMM_LEN); > + __entry->pid = task_pid_nr(tsk); > + __entry->tgid = task_tgid_nr(tsk); > + __entry->ngid = task_numa_group_id(tsk); > + ), > + > + TP_printk("comm=%s pid=%d tgid=%d ngid=%d", > + __entry->comm, > + __entry->pid, > + __entry->tgid, > + __entry->ngid) > +); > + > +TRACE_EVENT(sched_numa_balance_end, > + > + TP_PROTO(struct task_struct *tsk, unsigned long scanned, unsigned long > migrated), > + > + TP_ARGS(tsk, scanned, migrated), > + > + TP_STRUCT__entry( > + __array(char, comm, TASK_COMM_LEN) > + __field(pid_t, pid) > + __field(pid_t, tgid) > + __field(pid_t, ngid) > + __field(unsigned long, migrated) > + __field(unsigned long, scanned) > + ), > + > + TP_fast_assign( > + memcpy(__entry->comm, tsk->comm, TASK_COMM_LEN); > + __entry->pid = task_pid_nr(tsk); > + __entry->tgid = task_tgid_nr(tsk); > + __entry->ngid = task_numa_group_id(tsk); > + __entry->migrated = migrated; > + __entry->scanned = scanned; > + ), > + > + TP_printk("comm=%s pid=%d tgid=%d ngid=%d scanned=%lu migrated=%lu", > + __entry->comm, > + __entry->pid, > + __entry->tgid, > + __entry->ngid, > + __entry->scanned, > + __entry->migrated) > +); > #endif /* CONFIG_NUMA_BALANCING */ > > /* > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 25970dbbb279..173c9c8397e2 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -3294,6 +3294,9 @@ static void task_numa_work(struct callback_head *work) > struct vm_area_struct *vma; > unsigned long start, end; > unsigned long nr_pte_updates = 0; > + unsigned long nr_scanned = 0; > + unsigned long total_migrated = 0; > + unsigned long total_scanned = 0; > long pages, virtpages; > struct vma_iterator vmi; > bool vma_pids_skipped; > @@ -3359,6 +3362,7 @@ static void task_numa_work(struct callback_head *work) > if (!mmap_read_trylock(mm)) > return; > > + trace_sched_numa_balance_start(p); > /* > * VMAs are skipped if the current PID has not trapped a fault within > * the VMA recently. Allow scanning to be forced if there is no > @@ -3477,6 +3481,10 @@ static void task_numa_work(struct callback_head *work) > end = min(end, vma->vm_end); > nr_pte_updates = change_prot_numa(vma, start, end); > > + nr_scanned = (end - start) >> PAGE_SHIFT; > + total_migrated += nr_pte_updates; > + total_scanned += nr_scanned; > + This will require the scheduler maintainers agreeing on this for acceptance. Will kprobes not due? -- Steve > /* > * Try to scan sysctl_numa_balancing_size worth of > * hpages that have at least one present PTE that > @@ -3486,8 +3494,8 @@ static void task_numa_work(struct callback_head *work) > * areas faster. > */ > if (nr_pte_updates) > - pages -= (end - start) >> PAGE_SHIFT; > - virtpages -= (end - start) >> PAGE_SHIFT; > + pages -= nr_scanned; > + virtpages -= nr_scanned; > > start = end; > if (pages <= 0 || virtpages <= 0) > @@ -3528,6 +3536,8 @@ static void task_numa_work(struct callback_head *work) > mm->numa_scan_offset = start; > else > reset_ptenuma_scan(p); > + > + trace_sched_numa_balance_end(p, total_scanned, total_migrated); > mmap_read_unlock(mm); > > /*
