RFR(L): 8195142: Refactor out card table from CardTableModRefBS to flatten the BarrierSet hierarchy

Thu Feb 22 18:30:10 UTC 2018

Thank you, Erik

I am old C++ guy and using template for just casting is overkill to me. 
You still specify <type> when you can just use cast (type). So what 
benefit template has in this case?

Otherwise looks good.

Thanks,
Vladimir

On 2/22/18 3:45 AM, Erik Österlund wrote:
> Hi Vladimir,
> 
> Thank you for having a look at this.
> 
> I created some utility functions in ci/ciUtilities.hpp to get the card 
> table:
> 
> jbyte* ci_card_table_address()
> template<T> T ci_card_table_address_as()
> 
> The compiler code has been updated to use these helpers instead to fetch 
> the card table in a consistent way.
> 
> Hope this is kind of what you had in mind?
> 
> New full webrev:
> http://cr.openjdk.java.net/~eosterlund/8195142/webrev.03/
> 
> New incremental webrev:
> http://cr.openjdk.java.net/~eosterlund/8195142/webrev.02_03/
> 
> Thanks,
> /Erik
> 
> On 2018-02-21 18:12, Vladimir Kozlov wrote:
>> Hi Erik,
>>
>> I looked on compiler and aot changes. I noticed repeated sequence in 
>> several files to get byte_map_base()
>>
>> +  BarrierSet* bs = Universe::heap()->barrier_set();
>> +  CardTableModRefBS* ctbs = barrier_set_cast<CardTableModRefBS>(bs);
>> +  CardTable* ct = ctbs->card_table();
>> +  assert(sizeof(*(ct->byte_map_base())) == sizeof(jbyte), "adjust 
>> this code");
>> +  LIR_Const* card_table_base = new LIR_Const(ct->byte_map_base());
>>
>> But sometimes it has the assert (graphKit.cpp) and sometimes does not 
>> (aotCodeHeap.cpp).
>>
>> Can you factor this sequence into one method which can be used in all 
>> such places?
>>
>> Thanks,
>> Vladimir
>>
>> On 2/21/18 3:33 AM, Erik Österlund wrote:
>>> Hi Erik,
>>>
>>> Thank you for reviewing this.
>>>
>>> New full webrev:
>>> http://cr.openjdk.java.net/~eosterlund/8195142/webrev.02/
>>>
>>> New incremental webrev:
>>> http://cr.openjdk.java.net/~eosterlund/8195142/webrev.01_02/
>>>
>>> On 2018-02-21 09:18, Erik Helin wrote:
>>>> Hi Erik,
>>>>
>>>> this is a very nice improvement, thanks for working on this!
>>>>
>>>> A few minor comments thus far:
>>>> - in stubGenerator_ppc.cpp:
>>>>   you seem to have lost a `const` in the refactoring
>>>
>>> Fixed.
>>>
>>>> - in psCardTable.hpp:
>>>>   I don't think card_mark_must_follow_store() is needed, since
>>>>   PSCardTable passes `false` for `conc_scan` to the CardTable
>>>>   constructor
>>>
>>> Fixed. I took the liberty of also making the condition for 
>>> card_mark_must_follow_store() more precise on CMS by making the 
>>> condition for scanned_concurrently consider whether 
>>> CMSPrecleaningEnabled is set or not (like other generated code does).
>>>
>>>> - in g1CollectedHeap.hpp:
>>>>   could you store the G1CardTable as a field in G1CollectedHeap? Also,
>>>>   could you name the "getter" just card_table()? (I see that
>>>>   g1_hot_card_cache method above, but that one should also be 
>>>> renamed to
>>>>   just hot_card_cache, but in another patch)
>>>
>>> Fixed.
>>>
>>>> - in cardTable.hpp and cardTable.cpp:
>>>>   could you use `hg cp` when constructing these files from
>>>>   cardTableModRefBS.{hpp,cpp} so the history is preserved?
>>>
>>> Yes, I will do this before pushing to make sure the history is 
>>> preserved.
>>>
>>> Thanks,
>>> /Erik
>>>
>>>>
>>>> Thanks,
>>>> Erik
>>>>
>>>> On 02/15/2018 10:31 AM, Erik Österlund wrote:
>>>>> Hi,
>>>>>
>>>>> Here is an updated revision of this webrev after internal feedback 
>>>>> from StefanK who helped looking through my changes - thanks a lot 
>>>>> for the help with that.
>>>>>
>>>>> The changes to the new revision are a bunch of minor clean up 
>>>>> changes, e.g. copy right headers, indentation issues, sorting 
>>>>> includes, adding/removing newlines, reverting an assert error 
>>>>> message, fixing constructor initialization orders, and things like 
>>>>> that.
>>>>>
>>>>> The problem I mentioned last time about the version number of our 
>>>>> repo not yet being bumped to 11 and resulting awkwardness in JVMCI 
>>>>> has been resolved by simply waiting. So now I changed the JVMCI 
>>>>> logic to get the card values from the new location in the 
>>>>> corresponding card tables when observing JDK version 11 or above.
>>>>>
>>>>> New full webrev (rebased onto a month fresher jdk-hs):
>>>>> http://cr.openjdk.java.net/~eosterlund/8195142/webrev.01/
>>>>>
>>>>> Incremental webrev (over the rebase):
>>>>> http://cr.openjdk.java.net/~eosterlund/8195142/webrev.00_01/
>>>>>
>>>>> This new version has run through hs-tier1-5 and jdk-tier1-3 without 
>>>>> any issues.
>>>>>
>>>>> Thanks,
>>>>> /Erik
>>>>>
>>>>> On 2018-01-17 13:54, Erik Österlund wrote:
>>>>>> Hi,
>>>>>>
>>>>>> Today, both Parallel, CMS and Serial share the same code for its 
>>>>>> card marking barrier. However, they have different requirements 
>>>>>> how to manage its card tables by the GC. And as the card table 
>>>>>> itself is embedded as a part of the CardTableModRefBS barrier set, 
>>>>>> this has led to an unnecessary inheritance hierarchy for 
>>>>>> CardTableModRefBS, where for example CardTableModRefBSForCTRS and 
>>>>>> CardTableExtension are CardTableModRefBS subclasses that do not 
>>>>>> change anything to do with the barriers.
>>>>>>
>>>>>> To clean up the code, there should really be a separate CardTable 
>>>>>> hierarchy that contains the differences how to manage the card 
>>>>>> table from the GC point of view, and simply let CardTableModRefBS 
>>>>>> have a CardTable. This would allow removing 
>>>>>> CardTableModRefBSForCTRS and CardTableExtension and their 
>>>>>> references from shared code (that really have nothing to do with 
>>>>>> the barriers, despite being barrier sets), and significantly 
>>>>>> simplify the barrier set code.
>>>>>>
>>>>>> This patch mechanically performs this refactoring. A new CardTable 
>>>>>> class has been created with a PSCardTable subclass for Parallel, a 
>>>>>> CardTableRS for CMS and Serial, and a G1CardTable for G1. All 
>>>>>> references to card tables and their values have been updated 
>>>>>> accordingly.
>>>>>>
>>>>>> This touches a lot of platform specific code, so would be 
>>>>>> fantastic if port maintainers could have a look that I have not 
>>>>>> broken anything.
>>>>>>
>>>>>> There is a slight problem that should be pointed out. There is an 
>>>>>> unfortunate interaction between Graal and hotspot. Graal needs to 
>>>>>> know the values of g1 young cards and dirty cards. This is queried 
>>>>>> in different ways in different versions of the JDK in the 
>>>>>> ||GraalHotSpotVMConfig.java file. Now these values will move from 
>>>>>> their barrier set class to their card table class. That means we 
>>>>>> have at least three cases how to find the correct values. There is 
>>>>>> one for JDK8, one for JDK9, and now a new one for JDK11. Except, 
>>>>>> we have not yet bumped the version number to 11 in the repo, and 
>>>>>> therefore it has to be from JDK10 - 11 for now and updated after 
>>>>>> incrementing the version number. But that means that it will be 
>>>>>> temporarily incompatible with JDK10. That is okay for our own copy 
>>>>>> of Graal, but can not be used by upstream Graal as they are given 
>>>>>> the choice whether to support the public JDK10 or the JDK11 that 
>>>>>> does not quite admit to being 11 yet. I chose the solution that 
>>>>>> works in our repository. I will notify Graal folks of this issue. 
>>>>>> In the long run, it would be nice if we could have a more solid 
>>>>>> interface here.
>>>>>>
>>>>>> However, as an added benefit, this changeset brings about a 
>>>>>> hundred copyright headers up to date, so others do not have to 
>>>>>> update them for a while.
>>>>>>
>>>>>> Bug:
>>>>>> https://bugs.openjdk.java.net/browse/JDK-8195142
>>>>>>
>>>>>> Webrev:
>>>>>> http://cr.openjdk.java.net/~eosterlund/8195142/webrev.00/
>>>>>>
>>>>>> Testing: mach5 hs-tier1-5 plus local AoT testing.
>>>>>>
>>>>>> Thanks,
>>>>>> /Erik
>>>>>
>>>
> 