Re: [PATCH tip/core/rcu 02/26] mm/mmap.c: Add cond_resched() for exit_mmap() CPU stalls
On Tue, Jun 23, 2020 at 01:55:08PM -0700, Paul E. McKenney wrote: [..] > > Just for my understanding, cond_resched_tasks_rcu_qs() may not help here > > because preemption is not disabled right? Still I see no harm in using it > > here either as it may give a slight speed up for tasks-RCU. > > The RCU-tasks stall-warning interval is ten minutes, and I have not yet > seen evidence that we are getting close to that. If we do, then yes, > a cond_resched_tasks_rcu_qs() might be in this code's future. But it > does add overhead, so we need to see the evidence first. Yes, true about that overhead. Ok, this is fine with me too, thanks :) - Joel
Re: [PATCH tip/core/rcu 02/26] mm/mmap.c: Add cond_resched() for exit_mmap() CPU stalls
On Tue, Jun 23, 2020 at 03:34:31PM -0400, Joel Fernandes wrote: > On Mon, Jun 22, 2020 at 05:21:23PM -0700, paul...@kernel.org wrote: > > From: "Paul E. McKenney" > > > > A large process running on a heavily loaded system can encounter the > > following RCU CPU stall warning: > > > > rcu: INFO: rcu_sched self-detected stall on CPU > > rcu: \x093-: (20998 ticks this GP) idle=4ea/1/0x4002 > > softirq=556558/556558 fqs=5190 > > \x09(t=21013 jiffies g=1005461 q=132576) > > NMI backtrace for cpu 3 > > CPU: 3 PID: 501900 Comm: aio-free-ring-w Kdump: loaded Not tainted > > 5.2.9-108_fbk12_rc3_3858_gb83b75af7909 #1 > > Hardware name: Wiwynn HoneyBadger/PantherPlus, BIOS HBM6.71 02/03/2016 > > Call Trace: > > > >dump_stack+0x46/0x60 > >nmi_cpu_backtrace.cold.3+0x13/0x50 > >? lapic_can_unplug_cpu.cold.27+0x34/0x34 > >nmi_trigger_cpumask_backtrace+0xba/0xca > >rcu_dump_cpu_stacks+0x99/0xc7 > >rcu_sched_clock_irq.cold.87+0x1aa/0x397 > >? tick_sched_do_timer+0x60/0x60 > >update_process_times+0x28/0x60 > >tick_sched_timer+0x37/0x70 > >__hrtimer_run_queues+0xfe/0x270 > >hrtimer_interrupt+0xf4/0x210 > >smp_apic_timer_interrupt+0x5e/0x120 > >apic_timer_interrupt+0xf/0x20 > > > > RIP: 0010:kmem_cache_free+0x223/0x300 > > Code: 88 00 00 00 0f 85 ca 00 00 00 41 8b 55 18 31 f6 f7 da 41 f6 45 0a > > 02 40 0f 94 c6 83 c6 05 9c 41 5e fa e8 a0 a7 01 00 41 56 9d <49> 8b 47 08 > > a8 03 0f 85 87 00 00 00 65 48 ff 08 e9 3d fe ff ff 65 > > RSP: 0018:c9000e8e3da8 EFLAGS: 0206 ORIG_RAX: ff13 > > RAX: 0002 RBX: 88861b9de960 RCX: 0030 > > RDX: fffe41e8 RSI: 60777fe3a100 RDI: 0001be18 > > RBP: ea00186e7780 R08: R09: > > R10: 88861b9dea28 R11: 7ffde000 R12: 81230a1f > > R13: 54684dc0 R14: 0206 R15: 547dbc00 > >? remove_vma+0x4f/0x60 > >remove_vma+0x4f/0x60 > >exit_mmap+0xd6/0x160 > >mmput+0x4a/0x110 > >do_exit+0x278/0xae0 > >? syscall_trace_enter+0x1d3/0x2b0 > >? handle_mm_fault+0xaa/0x1c0 > >do_group_exit+0x3a/0xa0 > >__x64_sys_exit_group+0x14/0x20 > >do_syscall_64+0x42/0x100 > >entry_SYSCALL_64_after_hwframe+0x44/0xa9 > > > > And on a PREEMPT=n kernel, the "while (vma)" loop in exit_mmap() can run > > for a very long time given a large process. This commit therefore adds > > a cond_resched() to this loop, providing RCU any needed quiescent states. > > > > Cc: Andrew Morton > > Cc: > > Signed-off-by: Paul E. McKenney > > --- > > mm/mmap.c | 1 + > > 1 file changed, 1 insertion(+) > > > > diff --git a/mm/mmap.c b/mm/mmap.c > > index 59a4682..972f839 100644 > > --- a/mm/mmap.c > > +++ b/mm/mmap.c > > @@ -3159,6 +3159,7 @@ void exit_mmap(struct mm_struct *mm) > > if (vma->vm_flags & VM_ACCOUNT) > > nr_accounted += vma_pages(vma); > > vma = remove_vma(vma); > > + cond_resched(); > > Reviewed-by: Joel Fernandes (Google) Thank you! I will apply this on my next rebase. > Just for my understanding, cond_resched_tasks_rcu_qs() may not help here > because preemption is not disabled right? Still I see no harm in using it > here either as it may give a slight speed up for tasks-RCU. The RCU-tasks stall-warning interval is ten minutes, and I have not yet seen evidence that we are getting close to that. If we do, then yes, a cond_resched_tasks_rcu_qs() might be in this code's future. But it does add overhead, so we need to see the evidence first. Thanx, Paul > thanks, > > - Joel > > > } > > vm_unacct_memory(nr_accounted); > > } > > -- > > 2.9.5 > >
Re: [PATCH tip/core/rcu 02/26] mm/mmap.c: Add cond_resched() for exit_mmap() CPU stalls
On Mon, Jun 22, 2020 at 05:21:23PM -0700, paul...@kernel.org wrote: > From: "Paul E. McKenney" > > A large process running on a heavily loaded system can encounter the > following RCU CPU stall warning: > > rcu: INFO: rcu_sched self-detected stall on CPU > rcu: \x093-: (20998 ticks this GP) idle=4ea/1/0x4002 > softirq=556558/556558 fqs=5190 > \x09(t=21013 jiffies g=1005461 q=132576) > NMI backtrace for cpu 3 > CPU: 3 PID: 501900 Comm: aio-free-ring-w Kdump: loaded Not tainted > 5.2.9-108_fbk12_rc3_3858_gb83b75af7909 #1 > Hardware name: Wiwynn HoneyBadger/PantherPlus, BIOS HBM6.71 02/03/2016 > Call Trace: > >dump_stack+0x46/0x60 >nmi_cpu_backtrace.cold.3+0x13/0x50 >? lapic_can_unplug_cpu.cold.27+0x34/0x34 >nmi_trigger_cpumask_backtrace+0xba/0xca >rcu_dump_cpu_stacks+0x99/0xc7 >rcu_sched_clock_irq.cold.87+0x1aa/0x397 >? tick_sched_do_timer+0x60/0x60 >update_process_times+0x28/0x60 >tick_sched_timer+0x37/0x70 >__hrtimer_run_queues+0xfe/0x270 >hrtimer_interrupt+0xf4/0x210 >smp_apic_timer_interrupt+0x5e/0x120 >apic_timer_interrupt+0xf/0x20 > > RIP: 0010:kmem_cache_free+0x223/0x300 > Code: 88 00 00 00 0f 85 ca 00 00 00 41 8b 55 18 31 f6 f7 da 41 f6 45 0a 02 > 40 0f 94 c6 83 c6 05 9c 41 5e fa e8 a0 a7 01 00 41 56 9d <49> 8b 47 08 a8 03 > 0f 85 87 00 00 00 65 48 ff 08 e9 3d fe ff ff 65 > RSP: 0018:c9000e8e3da8 EFLAGS: 0206 ORIG_RAX: ff13 > RAX: 0002 RBX: 88861b9de960 RCX: 0030 > RDX: fffe41e8 RSI: 60777fe3a100 RDI: 0001be18 > RBP: ea00186e7780 R08: R09: > R10: 88861b9dea28 R11: 7ffde000 R12: 81230a1f > R13: 54684dc0 R14: 0206 R15: 547dbc00 >? remove_vma+0x4f/0x60 >remove_vma+0x4f/0x60 >exit_mmap+0xd6/0x160 >mmput+0x4a/0x110 >do_exit+0x278/0xae0 >? syscall_trace_enter+0x1d3/0x2b0 >? handle_mm_fault+0xaa/0x1c0 >do_group_exit+0x3a/0xa0 >__x64_sys_exit_group+0x14/0x20 >do_syscall_64+0x42/0x100 >entry_SYSCALL_64_after_hwframe+0x44/0xa9 > > And on a PREEMPT=n kernel, the "while (vma)" loop in exit_mmap() can run > for a very long time given a large process. This commit therefore adds > a cond_resched() to this loop, providing RCU any needed quiescent states. > > Cc: Andrew Morton > Cc: > Signed-off-by: Paul E. McKenney > --- > mm/mmap.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/mm/mmap.c b/mm/mmap.c > index 59a4682..972f839 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -3159,6 +3159,7 @@ void exit_mmap(struct mm_struct *mm) > if (vma->vm_flags & VM_ACCOUNT) > nr_accounted += vma_pages(vma); > vma = remove_vma(vma); > + cond_resched(); Reviewed-by: Joel Fernandes (Google) Just for my understanding, cond_resched_tasks_rcu_qs() may not help here because preemption is not disabled right? Still I see no harm in using it here either as it may give a slight speed up for tasks-RCU. thanks, - Joel > } > vm_unacct_memory(nr_accounted); > } > -- > 2.9.5 >
Re: [PATCH tip/core/rcu 02/26] mm/mmap.c: Add cond_resched() for exit_mmap() CPU stalls
On Mon, Jun 22, 2020 at 05:47:19PM -0700, Shakeel Butt wrote: > On Mon, Jun 22, 2020 at 5:22 PM wrote: > > > > From: "Paul E. McKenney" > > > > A large process running on a heavily loaded system can encounter the > > following RCU CPU stall warning: > > > > rcu: INFO: rcu_sched self-detected stall on CPU > > rcu: \x093-: (20998 ticks this GP) idle=4ea/1/0x4002 > > softirq=556558/556558 fqs=5190 > > \x09(t=21013 jiffies g=1005461 q=132576) > > NMI backtrace for cpu 3 > > CPU: 3 PID: 501900 Comm: aio-free-ring-w Kdump: loaded Not tainted > > 5.2.9-108_fbk12_rc3_3858_gb83b75af7909 #1 > > Hardware name: Wiwynn HoneyBadger/PantherPlus, BIOS HBM6.71 02/03/2016 > > Call Trace: > > > >dump_stack+0x46/0x60 > >nmi_cpu_backtrace.cold.3+0x13/0x50 > >? lapic_can_unplug_cpu.cold.27+0x34/0x34 > >nmi_trigger_cpumask_backtrace+0xba/0xca > >rcu_dump_cpu_stacks+0x99/0xc7 > >rcu_sched_clock_irq.cold.87+0x1aa/0x397 > >? tick_sched_do_timer+0x60/0x60 > >update_process_times+0x28/0x60 > >tick_sched_timer+0x37/0x70 > >__hrtimer_run_queues+0xfe/0x270 > >hrtimer_interrupt+0xf4/0x210 > >smp_apic_timer_interrupt+0x5e/0x120 > >apic_timer_interrupt+0xf/0x20 > > > > RIP: 0010:kmem_cache_free+0x223/0x300 > > Code: 88 00 00 00 0f 85 ca 00 00 00 41 8b 55 18 31 f6 f7 da 41 f6 45 0a > > 02 40 0f 94 c6 83 c6 05 9c 41 5e fa e8 a0 a7 01 00 41 56 9d <49> 8b 47 08 > > a8 03 0f 85 87 00 00 00 65 48 ff 08 e9 3d fe ff ff 65 > > RSP: 0018:c9000e8e3da8 EFLAGS: 0206 ORIG_RAX: ff13 > > RAX: 0002 RBX: 88861b9de960 RCX: 0030 > > RDX: fffe41e8 RSI: 60777fe3a100 RDI: 0001be18 > > RBP: ea00186e7780 R08: R09: > > R10: 88861b9dea28 R11: 7ffde000 R12: 81230a1f > > R13: 54684dc0 R14: 0206 R15: 547dbc00 > >? remove_vma+0x4f/0x60 > >remove_vma+0x4f/0x60 > >exit_mmap+0xd6/0x160 > >mmput+0x4a/0x110 > >do_exit+0x278/0xae0 > >? syscall_trace_enter+0x1d3/0x2b0 > >? handle_mm_fault+0xaa/0x1c0 > >do_group_exit+0x3a/0xa0 > >__x64_sys_exit_group+0x14/0x20 > >do_syscall_64+0x42/0x100 > >entry_SYSCALL_64_after_hwframe+0x44/0xa9 > > > > And on a PREEMPT=n kernel, the "while (vma)" loop in exit_mmap() can run > > for a very long time given a large process. This commit therefore adds > > a cond_resched() to this loop, providing RCU any needed quiescent states. > > > > Cc: Andrew Morton > > Cc: > > Signed-off-by: Paul E. McKenney > > We have exactly the same change in our internal kernel since 2018. We > mostly observed the need_resched warnings on the processes mapping the > hugetlbfs. > > Reviewed-by: Shakeel Butt Thank you very much, I will apply your Reviewed-by on the next rebase. Any other patches we should know about? ;-) Thanx, Paul > > --- > > mm/mmap.c | 1 + > > 1 file changed, 1 insertion(+) > > > > diff --git a/mm/mmap.c b/mm/mmap.c > > index 59a4682..972f839 100644 > > --- a/mm/mmap.c > > +++ b/mm/mmap.c > > @@ -3159,6 +3159,7 @@ void exit_mmap(struct mm_struct *mm) > > if (vma->vm_flags & VM_ACCOUNT) > > nr_accounted += vma_pages(vma); > > vma = remove_vma(vma); > > + cond_resched(); > > } > > vm_unacct_memory(nr_accounted); > > } > > -- > > 2.9.5 > >
Re: [PATCH tip/core/rcu 02/26] mm/mmap.c: Add cond_resched() for exit_mmap() CPU stalls
On Mon, Jun 22, 2020 at 5:22 PM wrote: > > From: "Paul E. McKenney" > > A large process running on a heavily loaded system can encounter the > following RCU CPU stall warning: > > rcu: INFO: rcu_sched self-detected stall on CPU > rcu: \x093-: (20998 ticks this GP) idle=4ea/1/0x4002 > softirq=556558/556558 fqs=5190 > \x09(t=21013 jiffies g=1005461 q=132576) > NMI backtrace for cpu 3 > CPU: 3 PID: 501900 Comm: aio-free-ring-w Kdump: loaded Not tainted > 5.2.9-108_fbk12_rc3_3858_gb83b75af7909 #1 > Hardware name: Wiwynn HoneyBadger/PantherPlus, BIOS HBM6.71 02/03/2016 > Call Trace: > >dump_stack+0x46/0x60 >nmi_cpu_backtrace.cold.3+0x13/0x50 >? lapic_can_unplug_cpu.cold.27+0x34/0x34 >nmi_trigger_cpumask_backtrace+0xba/0xca >rcu_dump_cpu_stacks+0x99/0xc7 >rcu_sched_clock_irq.cold.87+0x1aa/0x397 >? tick_sched_do_timer+0x60/0x60 >update_process_times+0x28/0x60 >tick_sched_timer+0x37/0x70 >__hrtimer_run_queues+0xfe/0x270 >hrtimer_interrupt+0xf4/0x210 >smp_apic_timer_interrupt+0x5e/0x120 >apic_timer_interrupt+0xf/0x20 > > RIP: 0010:kmem_cache_free+0x223/0x300 > Code: 88 00 00 00 0f 85 ca 00 00 00 41 8b 55 18 31 f6 f7 da 41 f6 45 0a 02 > 40 0f 94 c6 83 c6 05 9c 41 5e fa e8 a0 a7 01 00 41 56 9d <49> 8b 47 08 a8 03 > 0f 85 87 00 00 00 65 48 ff 08 e9 3d fe ff ff 65 > RSP: 0018:c9000e8e3da8 EFLAGS: 0206 ORIG_RAX: ff13 > RAX: 0002 RBX: 88861b9de960 RCX: 0030 > RDX: fffe41e8 RSI: 60777fe3a100 RDI: 0001be18 > RBP: ea00186e7780 R08: R09: > R10: 88861b9dea28 R11: 7ffde000 R12: 81230a1f > R13: 54684dc0 R14: 0206 R15: 547dbc00 >? remove_vma+0x4f/0x60 >remove_vma+0x4f/0x60 >exit_mmap+0xd6/0x160 >mmput+0x4a/0x110 >do_exit+0x278/0xae0 >? syscall_trace_enter+0x1d3/0x2b0 >? handle_mm_fault+0xaa/0x1c0 >do_group_exit+0x3a/0xa0 >__x64_sys_exit_group+0x14/0x20 >do_syscall_64+0x42/0x100 >entry_SYSCALL_64_after_hwframe+0x44/0xa9 > > And on a PREEMPT=n kernel, the "while (vma)" loop in exit_mmap() can run > for a very long time given a large process. This commit therefore adds > a cond_resched() to this loop, providing RCU any needed quiescent states. > > Cc: Andrew Morton > Cc: > Signed-off-by: Paul E. McKenney We have exactly the same change in our internal kernel since 2018. We mostly observed the need_resched warnings on the processes mapping the hugetlbfs. Reviewed-by: Shakeel Butt > --- > mm/mmap.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/mm/mmap.c b/mm/mmap.c > index 59a4682..972f839 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -3159,6 +3159,7 @@ void exit_mmap(struct mm_struct *mm) > if (vma->vm_flags & VM_ACCOUNT) > nr_accounted += vma_pages(vma); > vma = remove_vma(vma); > + cond_resched(); > } > vm_unacct_memory(nr_accounted); > } > -- > 2.9.5 >
[PATCH tip/core/rcu 02/26] mm/mmap.c: Add cond_resched() for exit_mmap() CPU stalls
From: "Paul E. McKenney" A large process running on a heavily loaded system can encounter the following RCU CPU stall warning: rcu: INFO: rcu_sched self-detected stall on CPU rcu: \x093-: (20998 ticks this GP) idle=4ea/1/0x4002 softirq=556558/556558 fqs=5190 \x09(t=21013 jiffies g=1005461 q=132576) NMI backtrace for cpu 3 CPU: 3 PID: 501900 Comm: aio-free-ring-w Kdump: loaded Not tainted 5.2.9-108_fbk12_rc3_3858_gb83b75af7909 #1 Hardware name: Wiwynn HoneyBadger/PantherPlus, BIOS HBM6.71 02/03/2016 Call Trace: dump_stack+0x46/0x60 nmi_cpu_backtrace.cold.3+0x13/0x50 ? lapic_can_unplug_cpu.cold.27+0x34/0x34 nmi_trigger_cpumask_backtrace+0xba/0xca rcu_dump_cpu_stacks+0x99/0xc7 rcu_sched_clock_irq.cold.87+0x1aa/0x397 ? tick_sched_do_timer+0x60/0x60 update_process_times+0x28/0x60 tick_sched_timer+0x37/0x70 __hrtimer_run_queues+0xfe/0x270 hrtimer_interrupt+0xf4/0x210 smp_apic_timer_interrupt+0x5e/0x120 apic_timer_interrupt+0xf/0x20 RIP: 0010:kmem_cache_free+0x223/0x300 Code: 88 00 00 00 0f 85 ca 00 00 00 41 8b 55 18 31 f6 f7 da 41 f6 45 0a 02 40 0f 94 c6 83 c6 05 9c 41 5e fa e8 a0 a7 01 00 41 56 9d <49> 8b 47 08 a8 03 0f 85 87 00 00 00 65 48 ff 08 e9 3d fe ff ff 65 RSP: 0018:c9000e8e3da8 EFLAGS: 0206 ORIG_RAX: ff13 RAX: 0002 RBX: 88861b9de960 RCX: 0030 RDX: fffe41e8 RSI: 60777fe3a100 RDI: 0001be18 RBP: ea00186e7780 R08: R09: R10: 88861b9dea28 R11: 7ffde000 R12: 81230a1f R13: 54684dc0 R14: 0206 R15: 547dbc00 ? remove_vma+0x4f/0x60 remove_vma+0x4f/0x60 exit_mmap+0xd6/0x160 mmput+0x4a/0x110 do_exit+0x278/0xae0 ? syscall_trace_enter+0x1d3/0x2b0 ? handle_mm_fault+0xaa/0x1c0 do_group_exit+0x3a/0xa0 __x64_sys_exit_group+0x14/0x20 do_syscall_64+0x42/0x100 entry_SYSCALL_64_after_hwframe+0x44/0xa9 And on a PREEMPT=n kernel, the "while (vma)" loop in exit_mmap() can run for a very long time given a large process. This commit therefore adds a cond_resched() to this loop, providing RCU any needed quiescent states. Cc: Andrew Morton Cc: Signed-off-by: Paul E. McKenney --- mm/mmap.c | 1 + 1 file changed, 1 insertion(+) diff --git a/mm/mmap.c b/mm/mmap.c index 59a4682..972f839 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -3159,6 +3159,7 @@ void exit_mmap(struct mm_struct *mm) if (vma->vm_flags & VM_ACCOUNT) nr_accounted += vma_pages(vma); vma = remove_vma(vma); + cond_resched(); } vm_unacct_memory(nr_accounted); } -- 2.9.5
