RFR(XXS): 8029091: Bug in calculation of code cache sweeping interval

[Vladimir Kozlov]

On other hand ReservedCodeCacheSize can't be big since there is 2Gb limit. So it is small int value.
That in mind the fix is good.

Thanks,
Vladimir

On 11/25/13 9:33 AM, Vladimir Kozlov wrote:
> Albert,
>
> What if you use double type for calculations?:
>
> +     const double max_wait_time = (double)ReservedCodeCacheSize / (16 * M);
>
> Thanks,
> Vladimir
>
> On 11/25/13 5:27 AM, Albert Noll wrote:
>> Hi all,
>>
>> could I have reviews for this small patch?
>>
>> Bug: _
>> _https://bugs.openjdk.java.net/browse/JDK-8029091
>>
>> Webrev:
>> http://cr.openjdk.java.net/~anoll/8029091/webrev.00/
>>
>> Problem:
>> The calculation of 'wait_until_next_sweep' in 'NMethodSweeper::possibly_sweep() {}' has a signed
>> to unsigned conversion bug. The calculation is currently done as follows:
>>
>> double wait_until_next_sweep = (ReservedCodeCacheSize / (16 * M)) - time_since_last_sweep -
>> CodeCache::reverse_free_ratio();
>>
>> Since the type of 'ReservedCodeCacheSize' (uintx) has a higher rank than 'time_since_last_sleep' (int) and
>> 'time_since_last_sweep' can be larger than ' (ReservedCodeCacheSize / (16 * M))' there is an underflow. Consequently,
>> 'wait_until_next_sweep' is assigned a wrong value, which disables the intended periodic code cache sweeps.
>>
>> Solution:
>> Use only signed types for the calculation of 'wait_until_next_sweep'. Furthermore, an assert checks that
>> 'wait_until_next_sweep' is never larger than ' (ReservedCodeCacheSize / (16 * M))', which is the
>> maximum time between two sweeps.
>>
>>
>> Many thanks in advance,
>> Albert