Messages in this thread | | | Date | Wed, 22 Oct 2014 16:41:56 +0900 | From | Yasuaki Ishimatsu <> | Subject | Re: [PATCH v3] sched/fair: Care divide error in update_task_scan_period() |
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(2014/10/22 16:09), Wanpeng Li wrote: > 10/22/14, 3:04 PM, Yasuaki Ishimatsu: >> While offling node by hot removing memory, the following divide error >> occurs: >> >> divide error: 0000 [#1] SMP >> [...] >> Call Trace: >> [...] handle_mm_fault >> [...] ? try_to_wake_up >> [...] ? wake_up_state >> [...] __do_page_fault >> [...] ? do_futex >> [...] ? put_prev_entity >> [...] ? __switch_to >> [...] do_page_fault >> [...] page_fault >> [...] >> RIP [<ffffffff810a7081>] task_numa_fault >> RSP <ffff88084eb2bcb0> >> >> The issue occurs as follows: >> 1. When page fault occurs and page is allocated from node 1, >> task_struct->numa_faults_buffer_memory[] of node 1 is >> incremented and p->numa_faults_locality[] is also incremented >> as follows: >> >> o numa_faults_buffer_memory[] o numa_faults_locality[] >> NR_NUMA_HINT_FAULT_TYPES >> | 0 | 1 | >> ---------------------------------- ---------------------- >> node 0 | 0 | 0 | remote | 0 | >> node 1 | 0 | 1 | locale | 1 | >> ---------------------------------- ---------------------- >> >> 2. node 1 is offlined by hot removing memory. >> >> 3. When page fault occurs, fault_types[] is calculated by using >> p->numa_faults_buffer_memory[] of all online nodes in >> task_numa_placement(). But node 1 was offline by step 2. So >> the fault_types[] is calculated by using only >> p->numa_faults_buffer_memory[] of node 0. So both of fault_types[] >> are set to 0. >> >> 4. The values(0) of fault_types[] pass to update_task_scan_period(). >> >> 5. numa_faults_locality[1] is set to 1. So the following division is >> calculated. >> >> static void update_task_scan_period(struct task_struct *p, >> unsigned long shared, unsigned long private){ >> ... >> ratio = DIV_ROUND_UP(private * NUMA_PERIOD_SLOTS, (private + shared)); >> } >> >> 6. But both of private and shared are set to 0. So divide error >> occurs here. >> >> The divide error is rare case because the trigger is node offline. >> This patch always increments denominator for avoiding divide error. >> >> Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com> > > Reviewed-by: Wanpeng Li <wanpeng.li@linux.intel.com>
Thank you for your review.
Thanks, Yasuaki Ishimatsu
> >> --- >> v2: >> - Simply increment a denominator >> >> kernel/sched/fair.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> index 0b069bf..f3b492d 100644 >> --- a/kernel/sched/fair.c >> +++ b/kernel/sched/fair.c >> @@ -1520,7 +1520,7 @@ static void update_task_scan_period(struct task_struct *p, >> * scanning faster if shared accesses dominate as it may >> * simply bounce migrations uselessly >> */ >> - ratio = DIV_ROUND_UP(private * NUMA_PERIOD_SLOTS, (private + shared)); >> + ratio = DIV_ROUND_UP(private * NUMA_PERIOD_SLOTS, (private + shared + 1)); >> diff = (diff * ratio) / NUMA_PERIOD_SLOTS; >> } >> >
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