RFR(s): 8152176: Big ParGCCardsPerStrideChunk values can cause overflow for CMS GC
sangheon.kim at oracle.com
Tue Mar 29 19:07:00 UTC 2016
Thank you for reviewing this.
On 03/29/2016 10:49 AM, Jon Masamitsu wrote:
> I agree that we don't want to expose CardTableModRefBS::_last_valid_index
> but I'd consider making CardTableModRefBS::cards_required() public.
> That would remove the need to duplicate the calculation and it seems
> a reasonable question to ask the card table implementation how many
> cards it is going to require. I'll let other disagree if they like.
Good idea and changed to 'public'.
> Add in the message a little more about why the value is too large.
> 396 CommandLineError::print(verbose,
> 397 "ParGCCardsPerStrideChunk (" INTX_FORMAT ") "is too large for the
> heap size and " "must be "
> 398 "less than or equal to card table size (" SIZE_FORMAT ")\n",
> 399 value, card_table_size);
> I think a little more information here would help future maintainers so
> instead of
> 403 // If n_strides which is used with ParGCCardsPerStrideChunk is
> really large, we would face an overflow.
I updated the comment.
> This statement can overflow?
> 404 uintx n_strides = ParallelGCThreads * ParGCStridesPerThread;
Because above statement is checked not to overflow from
ParGCStridesPerThreadConstraintFunc() which is called before this
constraint function. (added this explanation as well)
> On 3/28/2016 3:50 PM, sangheon wrote:
>> Hi all,
>> Could I have some reviews for this change?
>> As very large value of ParGCCardsPerStrideChunk flag would result in
>> an overflow, we need a constraint function after memory
>> initialization. And the function will check the flag to be less than
>> of equal to the size of card table and not to make an overflow with
>> other stride factors(ParallelGCThreads and ParGCStridesPerThread).
>> CR: https://bugs.openjdk.java.net/browse/JDK-8152176
>> Webrev: http://cr.openjdk.java.net/~sangheki/8152176/webrev.00
>> Testing: JPRT, all runtime/commandline JTREG tests on all platforms
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