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Date: Thu, 13 May 2010 15:36:44 +0800
From: Miao Xie <miaox@...fujitsu.com>
To: Linux-Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -mm] cpuset,mm: make the write-side sleep if the read-side
is not running
Please ignore this mail. I'm sorry for my mistake.
Thanks
Miao
on 2010-5-13 15:26, Miao Xie wrote:
> on 2010-5-12 12:32, Andrew Morton wrote:
>> On Wed, 12 May 2010 15:20:51 +0800 Miao Xie <miaox@...fujitsu.com> wrote:
>>
>>> @@ -985,6 +984,7 @@ repeat:
>>> * for the read-side.
>>> */
>>> while (ACCESS_ONCE(tsk->mems_allowed_change_disable)) {
>>> + task_unlock(tsk);
>>> if (!task_curr(tsk))
>>> yield();
>>> goto repeat;
>>
>> Oh, I meant to mention that. No yield()s, please. Their duration is
>> highly unpredictable. Can we do something more deterministic here?
>
> 根据Andrew的指摘，我做了下面的patch，如果读端的进程处于内存分配过程中但不在运行，
> 则让负责修改tsk->mems_allowed的进程睡眠，等待读端结束内存分配操作。
>
> diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
> index 457ed76..d348c47 100644
> --- a/include/linux/cpuset.h
> +++ b/include/linux/cpuset.h
> @@ -117,7 +117,11 @@ static inline void put_mems_allowed(void)
> * nodemask.
> */
> smp_mb();
> - --ACCESS_ONCE(current->mems_allowed_change_disable);
> + if (!--ACCESS_ONCE(current->mems_allowed_change_disable)
> + && unlikely(current->mems_read_done)) {
> + complete(current->mems_read_done);
> + current->mems_read_done = NULL;
> + }
> }
>
> static inline void set_mems_allowed(nodemask_t nodemask)
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 66620fa..8699900 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1423,6 +1423,8 @@ struct task_struct {
> #ifdef CONFIG_CPUSETS
> nodemask_t mems_allowed; /* Protected by alloc_lock */
> int mems_allowed_change_disable;
> + /* for changing mems_allowed and mempolicy */
> + struct completion *mems_read_done;
> int cpuset_mem_spread_rotor;
> int cpuset_slab_spread_rotor;
> #endif
> @@ -2525,6 +2527,12 @@ static inline void inc_syscw(struct task_struct *tsk)
> extern void task_oncpu_function_call(struct task_struct *p,
> void (*func) (void *info), void *info);
>
> +/*
> + * Call the function if the target task is not executing right now
> + */
> +extern void task_notcurr_function_call(struct task_struct *p,
> + void (*func) (void *info), void *info);
> +
>
> #ifdef CONFIG_MM_OWNER
> extern void mm_update_next_owner(struct mm_struct *mm);
> diff --git a/kernel/cpuset.c b/kernel/cpuset.c
> index d243a22..a471ab2 100644
> --- a/kernel/cpuset.c
> +++ b/kernel/cpuset.c
> @@ -938,6 +938,20 @@ static void cpuset_migrate_mm(struct mm_struct *mm, const nodemask_t *from,
> guarantee_online_mems(task_cs(tsk),&tsk->mems_allowed);
> }
>
> +struct cpuset_task_info {
> + struct task_struct *tsk;
> + struct completion done;
> + int ret;
> +};
> +
> +void set_mems_read_done_for_task(void *_info)
> +{
> + struct cpuset_task_info *info = _info;
> +
> + info->tsk->mems_read_done = &info->done;
> + info->ret = 1;
> +}
> +
> /*
> * cpuset_change_task_nodemask - change task's mems_allowed and mempolicy
> * @tsk: the task to change
> @@ -950,6 +964,8 @@ static void cpuset_migrate_mm(struct mm_struct *mm, const nodemask_t *from,
> static void cpuset_change_task_nodemask(struct task_struct *tsk,
> nodemask_t *newmems)
> {
> + struct cpuset_task_info info;
> +
> repeat:
> /*
> * Allow tasks that have access to memory reserves because they have
> @@ -980,13 +996,23 @@ repeat:
> smp_mb();
>
> /*
> - * Allocating of memory is very fast, we needn't sleep when waitting
> - * for the read-side.
> + * If the read-side is running, we needn't sleep when waiting for the
> + * read-side because allocating page is very fast.
> */
> while (ACCESS_ONCE(tsk->mems_allowed_change_disable)) {
> task_unlock(tsk);
> - if (!task_curr(tsk))
> - yield();
> + if (!task_curr(tsk)) {
> + info.tsk = tsk;
> + init_completion(&info.done);
> + info.ret = 0;
> +
> + task_notcurr_function_call(tsk,
> + set_mems_read_done_for_task,
> + &info);
> + if (info.ret)
> + wait_for_completion(&info.done);
> + } else
> + cpu_relax();
> goto repeat;
> }
>
> diff --git a/kernel/fork.c b/kernel/fork.c
> index f4f0951..76a6ec8 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1090,6 +1090,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
> #ifdef CONFIG_CPUSETS
> p->cpuset_mem_spread_rotor = node_random(p->mems_allowed);
> p->cpuset_slab_spread_rotor = node_random(p->mems_allowed);
> + p->mems_read_done = NULL;
> #endif
> #ifdef CONFIG_TRACE_IRQFLAGS
> p->irq_events = 0;
> diff --git a/kernel/sched.c b/kernel/sched.c
> index e298c71..f839f8f 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -2217,6 +2217,35 @@ void task_oncpu_function_call(struct task_struct *p,
> preempt_enable();
> }
>
> +/**
> + * task_notcurr_function_call - call a function when a task isn't running
> + * @p: the task to evaluate
> + * @func: the function to be called
> + * @info: the function call argument
> + *
> + * Calls the function @func when the task is not currently running.
> + */
> +void task_notcurr_function_call(struct task_struct *p,
> + void (*func) (void *info), void *info)
> +{
> + struct rq *rq;
> + unsigned long flags;
> +
> + if (p == current)
> + return;
> +
> +#ifdef CONFIG_SMP
> + rq = task_rq_lock(p, &flags);
> + if (!task_curr(p))
> + func(info);
> + task_rq_unlock(rq, &flags);
> +#else
> + preempt_disable();
> + func(info);
> + preempt_enable();
> +#endif
> +}
> +
> #ifdef CONFIG_SMP
> /*
> * ->cpus_allowed is protected by either TASK_WAKING or rq->lock held.
>
> --
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