Re: [PATCH 01/14] resource limits: foundation for resource highwater tracking

[Topi Miettinen <toiwoton@gmail.com>]

On 07/15/16 12:49, Nicolas Dichtel wrote:
> Le 15/07/2016 12:35, Topi Miettinen a écrit :
>> There are many basic ways to control processes, including capabilities,
>> cgroups and resource limits. However, there are far fewer ways to find out
>> useful values for the limits, except blind trial and error.
>>
>> Prepare a foundation for resource highwater tracking.
>>
>> The collected highwater marks for the resources can be seen using
>> taskstats netlink interface.
>>
>> This depends on CONFIG_TASK_XACCT.
>>
>> Signed-off-by: Topi Miettinen <toiwoton@gmail.com>
>> ---
> [snip]
>> @@ -63,6 +65,8 @@ int print_task_context_switch_counts;
>>  /* Maximum number of cpus expected to be specified in a cpumask */
>>  #define MAX_CPUS	32
>>  
>> +#define TASKSTATS_VERSION_WITH_RESOURCE	9
>> +
>>  struct msgtemplate {
>>  	struct nlmsghdr n;
>>  	struct genlmsghdr g;
> [snip]
>> @@ -252,6 +276,22 @@ static void print_ioacct(struct taskstats *t)
>>  		(unsigned long long)t->cancelled_write_bytes);
>>  }
>>  
>> +static void print_racct(const struct taskstats *t)
>> +{
>> +	int i;
>> +
>> +	if (t->version < TASKSTATS_VERSION_WITH_RESOURCE) {
>> +		printf("kernel too old (%d < %d)\n", t->version,
>> +		       TASKSTATS_VERSION_WITH_RESOURCE);
>> +		return;
>> +	}
> 
> [snip]
>> diff --git a/include/uapi/linux/taskstats.h b/include/uapi/linux/taskstats.h
>> index 2466e55..8c65194 100644
>> --- a/include/uapi/linux/taskstats.h
>> +++ b/include/uapi/linux/taskstats.h
>> @@ -33,7 +33,7 @@
>>   */
>>  
>>  
>> -#define TASKSTATS_VERSION	8
>> +#define TASKSTATS_VERSION	9
>>  #define TS_COMM_LEN		32	/* should be >= TASK_COMM_LEN
>>  					 * in linux/sched.h */
>>  
>> @@ -163,6 +163,14 @@ struct taskstats {
>>  	/* Delay waiting for memory reclaim */
>>  	__u64	freepages_count;
>>  	__u64	freepages_delay_total;
>> +	/* Per-task storage I/O accounting ends */
>> +
>> +#define TASKSTATS_HAS_LIMIT_ACCOUNTING
>> +	/* Per-task resource accounting starts */
>> +	__u64   resource_hiwater[RLIM_NLIMITS]; /* high-watermark of
>> +						     RLIMIT
>> +						     resources */
>> +	/* Per-task resource accounting ends */
>>  };
> Why playing with version number? It complexifies the (userland) code and
> existing applications break when the kernel is updated.
> Goal of netlink is to be easily extensible. By adding a new attribute, existing
> userspace tools won't break.

I just followed this text in taskstats.h. Does that give wrong advice?

 * The struct is versioned. Newer versions should only add fields to
 * the bottom of the struct to maintain backward compatibility.
 *
 *
 * To add new fields
 *	a) bump up TASKSTATS_VERSION
 *	b) add comment indicating new version number at end of struct
 *	c) add new fields after version comment; maintain 64-bit alignment

-Topi

> 
> 
> Regards,
> Nicolas
>