RFR(s): 8145312: CMS: There is insufficient memory with CMSSamplingGrain=1 (original) (raw)

Jon Masamitsu jon.masamitsu at oracle.com
Tue Mar 8 22:02:24 UTC 2016

On 3/8/2016 11:47 AM, sangheon wrote:

Hi Jon,

Thanks for reviewing this. concurrentMarkSweepGeneration.cpp: line 606 edenchunkcapacity = (younggen->maxcapacity() + CMSSamplingGrain) / CMSSamplingGrain; If CMSSamplingGrain is larger than 'maxuintx - younggen->maxcapacity()', it will make an overflow. FYI, 'edenchunkcapacity' is 'sizet' and 'CMSSamplingGrain' is 'uintx'

Ok.

Changes look good then.

Jon

Thanks, Sangheon

On 03/08/2016 11:20 AM, Jon Masamitsu wrote: Sangheon,

http://cr.openjdk.java.net/~sangheki/8145312/webrev.00/src/share/vm/runtime/commandLineFlagConstraintsGC.cpp.frames.html

456 if (value > maxuintx - maxcapacity) { 457 CommandLineError::print(verbose, 458 "CMSSamplingGrain (" UINTXFORMAT ") must be " 459 "less than or equal to ergonomic maximum (" SIZEFORMAT ")\n", 460 value, maxuintx - maxcapacity); How did you decide to use the test "value > maxuintx - maxcapacity"? Jon On 3/8/2016 12:00 AM, sangheon wrote: Hi all, Could I have some reviews for CMSSamplingGrain flag? The flag is used to calculate points at which the young gen should be partitioned for doing parallel work, so it only makes sense to partition at a granularity equal to or larger than the object size. I am proposing to change the minimum value of CMSSamplingGrain from '1' to 'ObjectAlignmentInBytes'. (ObjectAlignmentInBytes has a range of [8, 256]). In addition, I added a constraint function to avoid an arithmetic overflow by its maximum value. CR: https://bugs.openjdk.java.net/browse/JDK-8145312 Webrev: http://cr.openjdk.java.net/~sangheki/8145312/webrev.00/ Testing: JPRT, RBT for all platforms including embedded Thanks, Sangheon

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