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Date: Thu, 13 May 2010 15:26:33 +0800
From: Miao Xie <miaox@...fujitsu.com>
To: Linux-Kernel <linux-kernel@...r.kernel.org>
Subject: [PATCH -mm] cpuset,mm: make the write-side sleep if the read-side
is not running
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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