Messages in this thread Patch in this message | | | Date | Sat, 02 Apr 2005 13:30:14 +1000 | From | Nick Piggin <> | Subject | [patch][rfc] optimise resched, idle task |
| |
Haven't finished (hardly started) the arch code for this yet (and probably broke ppc64), so it is just an RFC at this stage.
The large CC list is because it is a reasonably big change, so I hope one or two of you smart guys can see if it looks sound before I try to tackle the rest of the arch code and start asking for testers.
This actually improves performance noticably (ie. a % or so) on schedule / wakeup happy benchmarks (tbench, on a dual Xeon with HT using mwait idle).
-- SUSE Labs, Novell Inc. Make some changes to the NEED_RESCHED and POLLING_NRFLAG to reduce confusion, and make their semantics rigid. Also have preempt explicitly disabled in idle routines. Improves efficiency of resched_task and some cpu_idle routines.
* In resched_task: - TIF_NEED_RESCHED is only cleared with the task's runqueue lock held, and as we hold it during resched_task, then there is no need for an atomic test and set there. (The only time this may prevent an IPI is when the task's quantum expires in the timer interrupt - this is a very rare race to bother with in comparison with the cost).
- If TIF_NEED_RESCHED is set, then we don't need to do anything. It won't get unset until the task get's schedule()d off.
- If we are running on the same CPU as the task we resched, then set TIF_NEED_RESCHED and no further action is required.
- If we are running on another CPU, and TIF_POLLING_NRFLAG is *not* set after TIF_NEED_RESCHED has been set, then we need to send an IPI.
Using these rules, we are able to remove the test and set operation in resched_task, and make clear the previously vague semantics of POLLING_NRFLAG.
* In idle routines: - Enter cpu_idle with preempt disabled. When the need_resched() condition becomes true, explicitly call schedule(). This makes things a bit clearer (IMO), but haven't updated all architectures yet.
- Many do a test and clear of TIF_NEED_RESCHED for some reason. According to the resched_task rules, this isn't needed (and actually breaks the assumption that TIF_NEED_RESCHED is only cleared with the runqueue lock held). So remove that. Generally one less locked memory op when switching to the idle thread.
- Many idle routines clear TIF_POLLING_NRFLAG, and only set it in the inner most polling idle loops. The above resched_task semantics allow it to be set until before the last time need_resched() is checked before going into a halt requiring interrupt wakeup.
Many idle routines simply never enter such a halt, and so POLLING_NRFLAG can be always left set, completely eliminating resched IPIs when rescheduling the idle task.
POLLING_NRFLAG width can be increased, to reduce the chance of resched IPIs.
Index: linux-2.6/kernel/sched.c =================================================================== --- linux-2.6.orig/kernel/sched.c 2005-03-27 00:25:49.000000000 +1100 +++ linux-2.6/kernel/sched.c 2005-03-27 00:27:30.000000000 +1100 @@ -796,21 +796,28 @@ static void deactivate_task(struct task_ #ifdef CONFIG_SMP static void resched_task(task_t *p) { - int need_resched, nrpolling; + int cpu; assert_spin_locked(&task_rq(p)->lock); - /* minimise the chance of sending an interrupt to poll_idle() */ - nrpolling = test_tsk_thread_flag(p,TIF_POLLING_NRFLAG); - need_resched = test_and_set_tsk_thread_flag(p,TIF_NEED_RESCHED); - nrpolling |= test_tsk_thread_flag(p,TIF_POLLING_NRFLAG); + if (test_tsk_thread_flag(p, TIF_NEED_RESCHED)) + return; + + set_tsk_thread_flag(p, TIF_NEED_RESCHED); - if (!need_resched && !nrpolling && (task_cpu(p) != smp_processor_id())) - smp_send_reschedule(task_cpu(p)); + cpu = task_cpu(p); + if (cpu == smp_processor_id()) + return; + + /* NEED_RESCHED must be visible before we test POLLING_NRFLAG */ + smp_mb(); + if (!test_tsk_thread_flag(p, TIF_POLLING_NRFLAG)) + smp_send_reschedule(cpu); } #else static inline void resched_task(task_t *p) { + assert_spin_locked(&task_rq(p)->lock); set_tsk_need_resched(p); } #endif Index: linux-2.6/arch/i386/kernel/process.c =================================================================== --- linux-2.6.orig/arch/i386/kernel/process.c 2005-03-27 00:25:49.000000000 +1100 +++ linux-2.6/arch/i386/kernel/process.c 2005-03-27 00:27:30.000000000 +1100 @@ -95,14 +95,19 @@ EXPORT_SYMBOL(enable_hlt); */ void default_idle(void) { + local_irq_enable(); + if (!hlt_counter && boot_cpu_data.hlt_works_ok) { - local_irq_disable(); - if (!need_resched()) + clear_thread_flag(TIF_POLLING_NRFLAG); + smp_mb__after_clear_bit(); + while (!need_resched()) { + local_irq_disable(); safe_halt(); - else - local_irq_enable(); + } + set_thread_flag(TIF_POLLING_NRFLAG); } else { - cpu_relax(); + while (!need_resched()) + cpu_relax(); } } @@ -113,29 +118,14 @@ void default_idle(void) */ static void poll_idle (void) { - int oldval; - local_irq_enable(); - /* - * Deal with another CPU just having chosen a thread to - * run here: - */ - oldval = test_and_clear_thread_flag(TIF_NEED_RESCHED); - - if (!oldval) { - set_thread_flag(TIF_POLLING_NRFLAG); - asm volatile( - "2:" - "testl %0, %1;" - "rep; nop;" - "je 2b;" - : : "i"(_TIF_NEED_RESCHED), "m" (current_thread_info()->flags)); - - clear_thread_flag(TIF_POLLING_NRFLAG); - } else { - set_need_resched(); - } + asm volatile( + "2:" + "testl %0, %1;" + "rep; nop;" + "je 2b;" + : : "i"(_TIF_NEED_RESCHED), "m" (current_thread_info()->flags)); } /* @@ -146,25 +136,27 @@ static void poll_idle (void) */ void cpu_idle (void) { - int cpu = _smp_processor_id(); + int cpu = smp_processor_id(); + set_thread_flag(TIF_POLLING_NRFLAG); /* endless idle loop with no priority at all */ while (1) { - while (!need_resched()) { - void (*idle)(void); + void (*idle)(void); - if (cpu_isset(cpu, cpu_idle_map)) - cpu_clear(cpu, cpu_idle_map); - rmb(); - idle = pm_idle; + if (cpu_isset(cpu, cpu_idle_map)) + cpu_clear(cpu, cpu_idle_map); + rmb(); + idle = pm_idle; - if (!idle) - idle = default_idle; + if (!idle) + idle = default_idle; - irq_stat[cpu].idle_timestamp = jiffies; - idle(); - } + irq_stat[cpu].idle_timestamp = jiffies; + idle(); + + preempt_enable_no_resched(); schedule(); + preempt_disable(); } } @@ -195,15 +187,12 @@ static void mwait_idle(void) { local_irq_enable(); - if (!need_resched()) { - set_thread_flag(TIF_POLLING_NRFLAG); - do { - __monitor((void *)¤t_thread_info()->flags, 0, 0); - if (need_resched()) - break; - __mwait(0, 0); - } while (!need_resched()); - clear_thread_flag(TIF_POLLING_NRFLAG); + while (!need_resched()) { + __monitor((void *)¤t_thread_info()->flags, 0, 0); + smp_mb(); + if (need_resched()) + break; + __mwait(0, 0); } } Index: linux-2.6/init/main.c =================================================================== --- linux-2.6.orig/init/main.c 2005-03-27 00:25:49.000000000 +1100 +++ linux-2.6/init/main.c 2005-03-27 00:27:30.000000000 +1100 @@ -382,7 +382,7 @@ static void noinline rest_init(void) kernel_thread(init, NULL, CLONE_FS | CLONE_SIGHAND); numa_default_policy(); unlock_kernel(); - preempt_enable_no_resched(); + /* Don't re-enable preemption */ cpu_idle(); } Index: linux-2.6/arch/i386/kernel/apm.c =================================================================== --- linux-2.6.orig/arch/i386/kernel/apm.c 2005-03-27 00:25:49.000000000 +1100 +++ linux-2.6/arch/i386/kernel/apm.c 2005-03-27 00:27:30.000000000 +1100 @@ -767,8 +767,20 @@ static int set_system_power_state(u_shor static int apm_do_idle(void) { u32 eax; + u8 ret; + int idled = 0; - if (apm_bios_call_simple(APM_FUNC_IDLE, 0, 0, &eax)) { + clear_thread_flag(TIF_POLLING_NRFLAG); + smp_mb__after_clear_bit(); + if (!need_resched()) { + idled = 1; + ret = apm_bios_call_simple(APM_FUNC_IDLE, 0, 0, &eax); + } + set_thread_flag(TIF_POLLING_NRFLAG); + if (!idled) + return 0; + + if (ret) { static unsigned long t; /* This always fails on some SMP boards running UP kernels. Index: linux-2.6/drivers/acpi/processor_idle.c =================================================================== --- linux-2.6.orig/drivers/acpi/processor_idle.c 2005-03-27 00:25:49.000000000 +1100 +++ linux-2.6/drivers/acpi/processor_idle.c 2005-03-27 00:27:30.000000000 +1100 @@ -162,6 +162,14 @@ acpi_processor_power_activate ( return; } +static void acpi_safe_halt (void) +{ + clear_thread_flag(TIF_POLLING_NRFLAG); + smp_mb__after_clear_bit(); + while (!need_resched()) + safe_halt(); + set_thread_flag(TIF_POLLING_NRFLAG); +} static void acpi_processor_idle (void) { @@ -171,7 +179,7 @@ static void acpi_processor_idle (void) int sleep_ticks = 0; u32 t1, t2 = 0; - pr = processors[_smp_processor_id()]; + pr = processors[smp_processor_id()]; if (!pr) return; @@ -191,8 +199,13 @@ static void acpi_processor_idle (void) } cx = pr->power.state; - if (!cx) - goto easy_out; + if (!cx) { + if (pm_idle_save) + pm_idle_save(); + else + acpi_safe_halt(); + return; + } /* * Check BM Activity @@ -272,7 +285,8 @@ static void acpi_processor_idle (void) if (pm_idle_save) pm_idle_save(); else - safe_halt(); + acpi_safe_halt(); + /* * TBD: Can't get time duration while in C1, as resumes * go to an ISR rather than here. Need to instrument @@ -384,16 +398,6 @@ end: */ if (next_state != pr->power.state) acpi_processor_power_activate(pr, next_state); - - return; - - easy_out: - /* do C1 instead of busy loop */ - if (pm_idle_save) - pm_idle_save(); - else - safe_halt(); - return; } Index: linux-2.6/arch/i386/kernel/smpboot.c =================================================================== --- linux-2.6.orig/arch/i386/kernel/smpboot.c 2005-03-27 00:25:49.000000000 +1100 +++ linux-2.6/arch/i386/kernel/smpboot.c 2005-03-27 00:27:30.000000000 +1100 @@ -414,6 +414,8 @@ static int cpucount; */ static void __init start_secondary(void *unused) { + preempt_disable(); + /* * Dont put anything before smp_callin(), SMP * booting is too fragile that we want to limit the Index: linux-2.6/arch/x86_64/kernel/process.c =================================================================== --- linux-2.6.orig/arch/x86_64/kernel/process.c 2005-03-27 00:25:49.000000000 +1100 +++ linux-2.6/arch/x86_64/kernel/process.c 2005-03-27 00:27:30.000000000 +1100 @@ -84,12 +84,19 @@ EXPORT_SYMBOL(enable_hlt); */ void default_idle(void) { + local_irq_enable(); + if (!atomic_read(&hlt_counter)) { - local_irq_disable(); - if (!need_resched()) + clear_thread_flag(TIF_POLLING_NRFLAG); + smp_mb__after_clear_bit(); + while (!need_resched()) { + local_irq_disable(); safe_halt(); - else - local_irq_enable(); + } + set_thread_flag(TIF_POLLING_NRFLAG); + } else { + while (!need_resched()) + cpu_relax(); } } @@ -100,29 +107,16 @@ void default_idle(void) */ static void poll_idle (void) { - int oldval; - local_irq_enable(); - /* - * Deal with another CPU just having chosen a thread to - * run here: - */ - oldval = test_and_clear_thread_flag(TIF_NEED_RESCHED); - - if (!oldval) { - set_thread_flag(TIF_POLLING_NRFLAG); - asm volatile( - "2:" - "testl %0,%1;" - "rep; nop;" - "je 2b;" - : : - "i" (_TIF_NEED_RESCHED), - "m" (current_thread_info()->flags)); - } else { - set_need_resched(); - } + asm volatile( + "2:" + "testl %0,%1;" + "rep; nop;" + "je 2b;" + : : + "i" (_TIF_NEED_RESCHED), + "m" (current_thread_info()->flags)); } @@ -151,21 +145,23 @@ EXPORT_SYMBOL_GPL(cpu_idle_wait); void cpu_idle (void) { int cpu = smp_processor_id(); + set_thread_flag(TIF_POLLING_NRFLAG); /* endless idle loop with no priority at all */ while (1) { - while (!need_resched()) { - void (*idle)(void); + void (*idle)(void); - if (cpu_isset(cpu, cpu_idle_map)) - cpu_clear(cpu, cpu_idle_map); - rmb(); - idle = pm_idle; - if (!idle) - idle = default_idle; - idle(); - } + if (cpu_isset(cpu, cpu_idle_map)) + cpu_clear(cpu, cpu_idle_map); + rmb(); + idle = pm_idle; + if (!idle) + idle = default_idle; + idle(); + + preempt_enable_noresched(); schedule(); + preempt_disable(); } } @@ -180,15 +176,12 @@ static void mwait_idle(void) { local_irq_enable(); - if (!need_resched()) { - set_thread_flag(TIF_POLLING_NRFLAG); - do { - __monitor((void *)¤t_thread_info()->flags, 0, 0); - if (need_resched()) - break; - __mwait(0, 0); - } while (!need_resched()); - clear_thread_flag(TIF_POLLING_NRFLAG); + while (!need_resched()) { + __monitor((void *)¤t_thread_info()->flags, 0, 0); + smp_mb(); + if (need_resched()) + break; + __mwait(0, 0); } } Index: linux-2.6/arch/ppc64/kernel/idle.c =================================================================== --- linux-2.6.orig/arch/ppc64/kernel/idle.c 2005-03-27 00:25:49.000000000 +1100 +++ linux-2.6/arch/ppc64/kernel/idle.c 2005-03-27 00:27:30.000000000 +1100 @@ -77,6 +77,8 @@ static int iSeries_idle(void) long oldval; unsigned long CTRL; + set_thread_flag(TIF_POLLING_NRFLAG); + /* ensure iSeries run light will be out when idle */ clear_thread_flag(TIF_RUN_LIGHT); CTRL = mfspr(CTRLF); @@ -86,32 +88,21 @@ static int iSeries_idle(void) lpaca = get_paca(); while (1) { - if (lpaca->lppaca.shared_proc) { - if (ItLpQueue_isLpIntPending(lpaca->lpqueue_ptr)) - process_iSeries_events(); - if (!need_resched()) - yield_shared_processor(); - } else { - oldval = test_and_clear_thread_flag(TIF_NEED_RESCHED); - - if (!oldval) { - set_thread_flag(TIF_POLLING_NRFLAG); - - while (!need_resched()) { - HMT_medium(); - if (ItLpQueue_isLpIntPending(lpaca->lpqueue_ptr)) - process_iSeries_events(); - HMT_low(); - } - + while (!need_resched()) { + HMT_low(); + if (ItLpQueue_isLpIntPending(lpaca->lpqueue_ptr)) { HMT_medium(); - clear_thread_flag(TIF_POLLING_NRFLAG); - } else { - set_need_resched(); + process_iSeries_events(); + HMT_low(); } + if (lpaca->lppaca.shared_proc) + yield_shared_processor(); } + HMT_medium(); + preempt_enable_no_resched(); schedule(); + preempt_disable(); } return 0; @@ -123,30 +114,23 @@ static int default_idle(void) { long oldval; unsigned int cpu = smp_processor_id(); - + set_thread_flag(TIF_POLLING_NRFLAG); + while (1) { - oldval = test_and_clear_thread_flag(TIF_NEED_RESCHED); - - if (!oldval) { - set_thread_flag(TIF_POLLING_NRFLAG); - - while (!need_resched() && !cpu_is_offline(cpu)) { - barrier(); - /* - * Go into low thread priority and possibly - * low power mode. - */ - HMT_low(); - HMT_very_low(); - } - - HMT_medium(); - clear_thread_flag(TIF_POLLING_NRFLAG); - } else { - set_need_resched(); + while (!need_resched() && !cpu_is_offline(cpu)) { + barrier(); + /* + * Go into low thread priority and possibly + * low power mode. + */ + HMT_low(); + HMT_very_low(); } + HMT_medium(); + preempt_enable_no_resched(); schedule(); + preempt_disable(); if (cpu_is_offline(cpu) && system_state == SYSTEM_RUNNING) cpu_die(); } @@ -166,6 +150,7 @@ int dedicated_idle(void) unsigned long *smt_snooze_delay = &__get_cpu_var(smt_snooze_delay); unsigned int cpu = smp_processor_id(); + set_thread_flag(TIF_POLLING_NRFLAG); ppaca = &paca[cpu ^ 1]; while (1) { @@ -175,66 +160,67 @@ int dedicated_idle(void) */ lpaca->lppaca.idle = 1; - oldval = test_and_clear_thread_flag(TIF_NEED_RESCHED); - if (!oldval) { - set_thread_flag(TIF_POLLING_NRFLAG); - start_snooze = __get_tb() + + start_snooze = __get_tb() + *smt_snooze_delay * tb_ticks_per_usec; - while (!need_resched() && !cpu_is_offline(cpu)) { - /* - * Go into low thread priority and possibly - * low power mode. - */ - HMT_low(); - HMT_very_low(); - if (*smt_snooze_delay == 0 || - __get_tb() < start_snooze) - continue; + while (!need_resched() && !cpu_is_offline(cpu)) { + /* + * Go into low thread priority and possibly + * low power mode. + */ + HMT_low(); + HMT_very_low(); - HMT_medium(); + if (*smt_snooze_delay == 0 || __get_tb() < start_snooze) + continue; - if (!(ppaca->lppaca.idle)) { - local_irq_disable(); + HMT_medium(); - /* - * We are about to sleep the thread - * and so wont be polling any - * more. - */ - clear_thread_flag(TIF_POLLING_NRFLAG); - - /* - * SMT dynamic mode. Cede will result - * in this thread going dormant, if the - * partner thread is still doing work. - * Thread wakes up if partner goes idle, - * an interrupt is presented, or a prod - * occurs. Returning from the cede - * enables external interrupts. - */ - if (!need_resched()) - cede_processor(); - else - local_irq_enable(); - } else { - /* - * Give the HV an opportunity at the - * processor, since we are not doing - * any work. - */ - poll_pending(); - } - } + if (!(ppaca->lppaca.idle)) { + local_irq_disable(); - clear_thread_flag(TIF_POLLING_NRFLAG); - } else { - set_need_resched(); + /* + * We are about to sleep the thread + * and so wont be polling any + * more. + */ + clear_thread_flag(TIF_POLLING_NRFLAG); + + /* + * Must have TIF_POLLING_NRFLAG clear visible + * before checking need_resched + */ + smp_mb__after_clear_bit(); + + /* + * SMT dynamic mode. Cede will result + * in this thread going dormant, if the + * partner thread is still doing work. + * Thread wakes up if partner goes idle, + * an interrupt is presented, or a prod + * occurs. Returning from the cede + * enables external interrupts. + */ + if (!need_resched()) + cede_processor(); + else + local_irq_enable(); + set_thread_flag(TIF_POLLING_NRFLAG); + } else { + /* + * Give the HV an opportunity at the + * processor, since we are not doing + * any work. + */ + poll_pending(); + } } HMT_medium(); lpaca->lppaca.idle = 0; + preempt_enable_no_resched(); schedule(); + preempt_disable(); if (cpu_is_offline(cpu) && system_state == SYSTEM_RUNNING) cpu_die(); } @@ -245,6 +231,7 @@ static int shared_idle(void) { struct paca_struct *lpaca = get_paca(); unsigned int cpu = smp_processor_id(); + set_thread_flag(TIF_POLLING_NRFLAG); while (1) { /* @@ -256,6 +243,9 @@ static int shared_idle(void) while (!need_resched() && !cpu_is_offline(cpu)) { local_irq_disable(); + clear_thread_flag(TIF_POLLING_NRFLAG); + smp_mb__after_clear_bit(); + /* * Yield the processor to the hypervisor. We return if * an external interrupt occurs (which are driven prior @@ -270,11 +260,14 @@ static int shared_idle(void) cede_processor(); else local_irq_enable(); + set_thread_flag(TIF_POLLING_NRFLAG); } HMT_medium(); lpaca->lppaca.idle = 0; + preempt_enable_no_resched(); schedule(); + preempt_disable(); if (cpu_is_offline(smp_processor_id()) && system_state == SYSTEM_RUNNING) cpu_die(); @@ -289,10 +282,12 @@ static int native_idle(void) { while(1) { /* check CPU type here */ - if (!need_resched()) + while (!need_resched()) power4_idle(); - if (need_resched()) - schedule(); + + preempt_enable_no_resched(); + schedule(); + preempt_disable(); if (cpu_is_offline(_smp_processor_id()) && system_state == SYSTEM_RUNNING) Index: linux-2.6/arch/ia64/kernel/process.c =================================================================== --- linux-2.6.orig/arch/ia64/kernel/process.c 2005-03-27 00:25:49.000000000 +1100 +++ linux-2.6/arch/ia64/kernel/process.c 2005-03-27 00:27:30.000000000 +1100 @@ -188,11 +188,16 @@ default_idle (void) { unsigned long pmu_active = ia64_getreg(_IA64_REG_PSR) & (IA64_PSR_PP | IA64_PSR_UP); - while (!need_resched()) - if (pal_halt && !pmu_active) + if (pal_halt && !pmu_active) { + clear_thread_flag(TIF_POLLING_NRFLAG); + smp_mb__after_clear_bit(); + while (!need_resched()) safe_halt(); - else + set_thread_flag(TIF_POLLING_NRFLAG); + } else { + while (!need_resched()) cpu_relax(); + } } #ifdef CONFIG_HOTPLUG_CPU @@ -251,35 +256,36 @@ cpu_idle (void) { void (*mark_idle)(int) = ia64_mark_idle; int cpu = smp_processor_id(); + set_thread_flag(TIF_POLLING_NRFLAG); /* endless idle loop with no priority at all */ while (1) { + void (*idle)(void); + if (cpu_isset(cpu, cpu_idle_map)) + cpu_clear(cpu, cpu_idle_map); + rmb(); + idle = pm_idle; + if (!idle) + idle = default_idle; + + if (!need_resched()) { #ifdef CONFIG_SMP - if (!need_resched()) min_xtp(); #endif - while (!need_resched()) { - void (*idle)(void); - if (mark_idle) (*mark_idle)(1); - - if (cpu_isset(cpu, cpu_idle_map)) - cpu_clear(cpu, cpu_idle_map); - rmb(); - idle = pm_idle; - if (!idle) - idle = default_idle; (*idle)(); - } - - if (mark_idle) - (*mark_idle)(0); - + if (mark_idle) + (*mark_idle)(0); #ifdef CONFIG_SMP - normal_xtp(); + normal_xtp(); #endif + } + + preempt_enable_no_resched(); schedule(); + preempt_disable(); + check_pgt_cache(); if (cpu_is_offline(smp_processor_id())) play_dead(); Index: linux-2.6/arch/ia64/kernel/smpboot.c =================================================================== --- linux-2.6.orig/arch/ia64/kernel/smpboot.c 2005-03-27 00:25:49.000000000 +1100 +++ linux-2.6/arch/ia64/kernel/smpboot.c 2005-03-27 00:27:30.000000000 +1100 @@ -343,6 +343,8 @@ smp_callin (void) int __devinit start_secondary (void *unused) { + preempt_disable(); + /* Early console may use I/O ports */ ia64_set_kr(IA64_KR_IO_BASE, __pa(ia64_iobase)); Index: linux-2.6/arch/ppc64/kernel/smp.c =================================================================== --- linux-2.6.orig/arch/ppc64/kernel/smp.c 2005-03-27 00:25:49.000000000 +1100 +++ linux-2.6/arch/ppc64/kernel/smp.c 2005-03-27 00:27:30.000000000 +1100 @@ -561,7 +561,10 @@ int __devinit __cpu_up(unsigned int cpu) /* Activate a secondary processor. */ int __devinit start_secondary(void *unused) { - unsigned int cpu = smp_processor_id(); + unsigned int cpu; + + preempt_disable(); + cpu = smp_processor_id(); atomic_inc(&init_mm.mm_count); current->active_mm = &init_mm; | |