RFR (XS): JDK-8076614: Add comment to ClearNoncleanCardWrapper::do_MemRegion()

[Bengt Rutisson]

Thanks for the reviews, Kim and StefanK!

Bengt


On 2015-04-08 09:36, Stefan Karlsson wrote:
>
>
> On 2015-04-02 23:35, Kim Barrett wrote:
>> On Apr 2, 2015, at 4:53 PM, Bengt Rutisson 
>> <bengt.rutisson at oracle.com> wrote:
>>>
>>> Hi all,
>>>
>>> Can I have a couple of reviews to add this comment to cardTableRS.cpp?
>>>
>>> https://bugs.openjdk.java.net/browse/JDK-8076614
>>>
>>> This was discussed during the review of "JDK-8076241: Remove unused 
>>> methods mod_card_iterate()    and non_clean_card_iterate_serial()", 
>>> see:
>>>
>>> http://mail.openjdk.java.net/pipermail/hotspot-gc-dev/2015-April/012661.html 
>>>
>>>
>>> For JDK-8076241 I removed this comment because it didn't make sense 
>>> anymore at the place where it used to be. We now agree that a better 
>>> place for
>>> it is close to the ClearNoncleanCardWrapper::do_MemRegion() method 
>>> because that still does backwards iteration of the card table.
>>>
>>> Since I am only adding a comment I think a diff is easier to review 
>>> than a webrev:
>>>
>>> diff --git a/src/share/vm/memory/cardTableRS.cpp 
>>> b/src/share/vm/memory/cardTableRS.cpp
>>> --- a/src/share/vm/memory/cardTableRS.cpp
>>> +++ b/src/share/vm/memory/cardTableRS.cpp
>>> @@ -176,7 +176,10 @@
>>> bool ClearNoncleanCardWrapper::is_word_aligned(jbyte* entry) {
>>> return (((intptr_t)entry) & (BytesPerWord-1)) == 0;
>>> }
>>> -
>>> +// The regions are visited in *decreasing* address order.
>>> +// This order aids with imprecise card marking, where a dirty
>>> +// card may cause scanning, and summarization marking, of objects
>>> +// that extend onto subsequent cards.
>>> void ClearNoncleanCardWrapper::do_MemRegion(MemRegion mr) {
>>> assert(mr.word_size() > 0, "Error");
>>> assert(_ct->is_aligned(mr.start()), "mr.start() should be card 
>>> aligned”);
>> Looks good.
>
> OK.
>
> StefanK
>
>>
>