[LTP] [PATCH] perf_event_open: improve the memory leak detection

[Martin Doucha]

On 17. 07. 24 10:31, Cyril Hrubis wrote:
> Hi!
>> +		/*
>> +		 * Every 1200000 iterations, calculate the difference in memory
>> +		 * availability. If the difference is greater than 10 * 1024 (10MB),
>> +		 * increment the sample counter and log the event.
>> +		 */
>> +		if ((i % 1200000) == 0) {
>> +			mem_avail = SAFE_READ_MEMINFO("MemAvailable:");
>> +			diff = mem_avail_prev - mem_avail;
>> +			diff_total += diff;
>> +
>> +			if (diff > 20 * 1024) {
> 
> Shouldn't this be 10 * 1024 or possibly slightly less than 10 * 1024?

This should be fine. The test leaks around 38MB between sample checks 
and over 350MB in a whole test run.

> 
>> +				sample++;
>> +				tst_res(TINFO, "MemAvailable decreased by %ld kB at iteration %d", diff, i);
>> +			}
>> +
>> +			mem_avail_prev = mem_avail;
>> +		}
>> +	}
>>   
>> -	if (diff > 50 * 1024)
>> -		tst_res(TFAIL, "Likely kernel memory leak detected");
>> +	if ((sample > 5) || (diff_total > 100 * 1024))
> 
> Maybe this can rather be if ((sample > 5) && (diff_total > 100 * 1024))
> 
> That means that the available memory has been eaten by something and
> that it happened more or less in a linear fashion when the program was
> running.

Imagine that some other process releases 300MB of memory while the test 
is running. If you change the || to &&, you'll get a false negative in 
that case. The sampling approach will protect against such interference.

That being said, if the available memory on your test system fluctuates 
by 100+MB during a test run that takes <10 seconds, I'd recommend 
investigating what's causing such fluctuation. On the test machine I 
used to verify this patch, I can see <10MB of difference before and 
after running the test on a fixed kernel.

> 
>> +		tst_res(TFAIL, "Likely kernel memory leak detected, total decrease: %ld kB", diff_total);
>>   	else
>>   		tst_res(TPASS, "No memory leak found");
>>   }
>> -- 
>> 2.45.2
>>
> 

-- 
Martin Doucha   mdoucha@suse.cz
SW Quality Engineer
SUSE LINUX, s.r.o.
CORSO IIa
Krizikova 148/34
186 00 Prague 8
Czech Republic