Re: [PATCH] mm: Introduce dedicated WQ_MEM_RECLAIM workqueue to do lru_add_drain_all

[Wang Sheng-Hui <shhuiw@foxmail.com>]

Tejun,


On 6/2/2016 10:39 PM, Tejun Heo wrote:
> On Thu, Jun 02, 2016 at 03:48:51PM +0800, Wang Sheng-Hui wrote:
>> +static int __init lru_init(void)
>> +{
>> +	lru_add_drain_wq = alloc_workqueue("lru-add-drain",
>> +		WQ_MEM_RECLAIM | WQ_UNBOUND, 0);
> Why is it unbound?
Sorry, I just pasted from other wq create statement.

WQ_MEM_RECLAIM is the key. Will drop WQ_UNBOUND in new version patch.


>> +	if (WARN(!lru_add_drain_wq,
>> +		"Failed to create workqueue lru_add_drain_wq"))
>> +		return -ENOMEM;
> I don't think we need an explicit warn here.  Doesn't error return
> from an init function trigger boot failure anyway?
Will drop the warn and return -ENOMEM directly on failure.
>> +	return 0;
>> +}
>> +early_initcall(lru_init);
>> +
>>  void lru_add_drain_all(void)
>>  {
>>  	static DEFINE_MUTEX(lock);
>>  	static struct cpumask has_work;
>>  	int cpu;
>>  
>> +	struct workqueue_struct *lru_wq = lru_add_drain_wq ?: system_wq;
>> +
>> +	WARN_ONCE(!lru_add_drain_wq,
>> +		"Use system_wq to do lru_add_drain_all()");
> Ditto.  The system is crashing for sure.  What's the point of this
> warning?
It's for above warn failure. Will crash instead of falling back to system_wq

>
> Thanks.
>
Thanks,
Sheng-Hui


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