RFR (M/L): 8010722 assert: failed: heap size is too big for compressed oops (possibly CR 8009778)

Coleen Phillimore coleen.phillimore at oracle.com
Tue Jun 4 18:51:50 PDT 2013

Thomas,  I don't think you posted an updated link.


On 6/4/2013 11:17 AM, Thomas Schatzl wrote:
> Hi all,
>    please have a look at a slightly updated version of this CR after
> comments from SQE and runtime.
> Changes:
> - moved the comment that explained the choice of a 100M default
> ClassMetaSpaceSize to the declaration of this value
> - changed the default size of ClassMetaSpaceSize to 128M as this is a
> value that results in less automatic resizing due to alignment (on
> request).
> Runtime intends to change this code in the future so that the
> ClassMetaSpaceSize is not dependent on java heap alignment any more (as
> far as I understood).
> - resolved a small merge conflict when updating to latest hotspot-gc:
> ParallelScavengeHeap::intra_heap_alignment() needs to be a static method
> to be used in a static context. This is not an issue here as it returns
> a constant value anyway.
> - added -XX:+UseParallelGC -XX:-UseParallelOldGC as gc combination to
> test in the test case. This required some changes in passing down these
> arguments to the tests themselves.
> Testing:
> jtreg tests, jprt
> There is a small introduction on the change below.
> On Tue, 2013-05-14 at 16:37 +0200, Thomas Schatzl wrote:
>> Hi all,
>>    can I have a review for the following change?
>> In argument processing related to ergonomically determining compressed
>> oops use, there were a few use-before-set issues leading to crashes that
>> this fix tries to resolve.
>> bugs.sun.com
>> http://bugs.sun.com/view_bug.do?bug_id=8010722
>> JIRA:
>> https://jbs.oracle.com/bugs/browse/JDK-8010722
>> webrev:
>> http://cr.openjdk.java.net/~tschatzl/8010722/webrev/
>> testing:
>> jprt, test cases
>> Here's a walkthrough of the changes:
>> As mentioned, the cause of this CR is that ergonomics for determining
>> the maximum java heap size usable for compressed oops uses variables
>> that are later changed ergonomically.
>> It is best to look at the changes beginning from
>> Arguments::set_ergonomics_flags(): the idea of this change is to avoid
>> later overflow, so the change tries to conservatively estimate sizes of
>> the non-java heap parts. The complication is that not even the later
>> effective alignment of these heap parts has been determined at this
>> point.
>> So the change first calculates the maximum possible heap alignment by
>> calling set_max_heap_alignment(); this size is influenced by OS page
>> sizes, so the change needs to initialize large pages by calling
>> os::large_page_init() in Arguments::parse(), before the call to
>> set_ergonomics_flags(). The maximum possible alignment is then
>> calculated by asking the active GC for its maximum alignment, as at this
>> point the GC has already been determined, the maximum page size, and
>> other requirements, like alignment for card table size etc.
>> Now the code can calculate the conservative estimate for actual maximum
>> heap for compressed oops used in set_use_compressed_oops(), by
>> subtracting the conservatively aligned sizes of the other heap parts.
>> (In Arguments::max_heap_for_compressed_oops()) The result is the maximum
>> possible heap that can use compressed oops, minus the aligned metaspace
>> size, minus the aligned null page size.
>> There is another circular dependency problem here, the metaspace size itself is later ergonomically sized; the change fixes this problem by anticipating that in Arguments::max_heap_for_compressed_oops(), using the same predicate for determining whether to ergonomically size it or not [this is CR8009778 I think].
>> The other changes are straightforward: the os_* changes result from that
>> large page initialization must be done earlier now; the changes in the
>> collectors themselves are simply about providing the collector's maximum
>> alignment. The change in Universe::reserve_heap() contains one assertion that checks whether the conservative estimate for alignment has been conservative enough earlier.
>> The test case tests test cases from the CR that work now, and additional
>> border cases related to ergonomically deciding heap size for compressed
>> oops.
>> One side effect of this change is that the ergonomically determined heap size is slighly smaller now (so that it always fits :).
> Thanks,
> Thomas

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