Re: [PATCH v4] mm, sysctl: make NUMA stats configurable

[kemi <kemi.wang@intel.com>]

On 2017a1'10ae??17ae?JPY 15:54, Michal Hocko wrote:
> On Tue 17-10-17 09:20:58, Kemi Wang wrote:
> [...]
> 
> Other than two remarks below, it looks good to me and it also looks
> simpler.
> 
>> diff --git a/mm/vmstat.c b/mm/vmstat.c
>> index 4bb13e7..e746ed1 100644
>> --- a/mm/vmstat.c
>> +++ b/mm/vmstat.c
>> @@ -32,6 +32,76 @@
>>  
>>  #define NUMA_STATS_THRESHOLD (U16_MAX - 2)
>>  
>> +#ifdef CONFIG_NUMA
>> +int sysctl_vm_numa_stat = ENABLE_NUMA_STAT;
>> +static DEFINE_MUTEX(vm_numa_stat_lock);
> 
> You can scope this mutex to the sysctl handler function
> 

OK, thanks.

>> +int sysctl_vm_numa_stat_handler(struct ctl_table *table, int write,
>> +		void __user *buffer, size_t *length, loff_t *ppos)
>> +{
>> +	int ret, oldval;
>> +
>> +	mutex_lock(&vm_numa_stat_lock);
>> +	if (write)
>> +		oldval = sysctl_vm_numa_stat;
>> +	ret = proc_dointvec(table, write, buffer, length, ppos);
>> +	if (ret || !write)
>> +		goto out;
>> +
>> +	if (oldval == sysctl_vm_numa_stat)
>> +		goto out;
>> +	else if (oldval == DISABLE_NUMA_STAT) {
> 
> So basically any value will enable numa stats. This means that we would
> never be able to extend this interface to e.g. auto mode (say value 2).
> I guess you meant to check sysctl_vm_numa_stat == ENABLE_NUMA_STAT?
> 

I meant to make it more general other than ENABLE_NUMA_STAT(non 0 is enough), 
but it will make it hard to scale, as you said.
So, it would be like this:
0 -- disable
1 -- enable
other value is invalid.

May add option 2 later for auto if necessary:)

>> +		static_branch_enable(&vm_numa_stat_key);
>> +		pr_info("enable numa statistics\n");
>> +	} else if (sysctl_vm_numa_stat == DISABLE_NUMA_STAT) {
>> +		static_branch_disable(&vm_numa_stat_key);
>> +		invalid_numa_statistics();
>> +		pr_info("disable numa statistics, and clear numa counters\n");
>> +	}
>> +
>> +out:
>> +	mutex_unlock(&vm_numa_stat_lock);
>> +	return ret;
>> +}
>> +#endif
>> +
>>  #ifdef CONFIG_VM_EVENT_COUNTERS
>>  DEFINE_PER_CPU(struct vm_event_state, vm_event_states) = {{0}};
>>  EXPORT_PER_CPU_SYMBOL(vm_event_states);
>> -- 
>> 2.7.4
>>
> 

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