RFR 8251557 Avoid dumping unused symbols/strings into the CDS archive

[calvin.cheung at oracle.com]

On 8/26/20 10:18 AM, Ioi Lam wrote:
>
>
> On 8/26/20 10:08 AM, Ioi Lam wrote:
>> Hi Calvin,
>>
>> Thanks for the review.
>>
>> On 8/26/20 9:40 AM, calvin.cheung at oracle.com wrote:
>>> Hi Ioi,
>>>
>>> The proposed change does make the code easier to read than before.
>>>
>>> I've comments on 2 files:
>>>
>>> heapShared.hpp:
>>>
>>> 42 class DumpedInternedStrings;
>>>
>>> Instead of forward declaration, is it possible to move the class 
>>> definition there since it is defined at the end of the file?
>>>
>>
>> I moved it as you suggested.
>
> Oops, sorry I hit "Send" too fast. DumpedInternedStrings depends on 
> function declared by HeapShared, so it must be declared after HeapShared
I see. So the change looks good.
>
> Thanks
> - Ioi
>
>
>>
>>> archiveBuilder.hpp:
>>>
>>> 37 class DumpRegion;
>>>
>>> The above forward declaration was removed but I think it's required 
>>> for the following:
>>>
>>
>> I removed the forward declaration because DumpRegion is declared in 
>> archiveUtils.hpp. Since JDK-8252056, archiveUtils.hpp is already 
>> included by archiveBuilder.hpp:
>>
>> http://hg.openjdk.java.net/jdk/jdk/rev/ba51bc0772ac
>>
>>>  132 DumpRegion* _rw_region;
>>>  133   DumpRegion* _ro_region;
>>>
>>> Also, the following constructor needs to be moved to 
>>> archiveBuilder.cpp or I got compile error about invalid use of 
>>> incomplete type 'class DumpRegion'.
>>>
>>>  158     OtherROAllocMark() {
>>>  159       _oldtop = _singleton->_ro_region->top();
>>>  160     }
>>>
>> Maybe you  applied the patch on a repo without the JDK-8252056 fix?
Right, I haven't updated my repo with the JDK-8252056 fix yet.
>>
>> I did find a problem with archiveUtils.hpp. It was using the Klass 
>> type without including klass.hpp, so I added
>>
>> diff -r 3920d1a29976 src/hotspot/share/memory/archiveBuilder.hpp
>> --- a/src/hotspot/share/memory/archiveBuilder.hpp    Wed Aug 19 
>> 14:14:20 2020 -0700
>> +++ b/src/hotspot/share/memory/archiveBuilder.hpp    Wed Aug 26 
>> 10:06:59 2020 -0700
>> @@ -27,6 +27,7 @@
>>
>>  #include "memory/archiveUtils.hpp"
>>  #include "memory/metaspaceClosure.hpp"
>> +#include "oops/klass.hpp"
>>  #include "utilities/bitMap.hpp"
>>  #include "utilities/growableArray.hpp"
>>  #include "utilities/hashtable.hpp"
>>
Since you're including klass.hpp, maybe the following forward 
declaration can be removed?

36 class Klass;

thanks,

Calvin

>>
>> Thanks
>> - Ioi
>>
>>
>>> thanks,
>>> Calvin
>>>
>>>
>>> On 8/19/20 2:39 PM, Ioi Lam wrote:
>>>> https://bugs.openjdk.java.net/browse/JDK-8251557
>>>> http://cr.openjdk.java.net/~iklam/jdk16/8251557-cds-dont-dump-unused-symbols.v01/ 
>>>>
>>>>
>>>> Part of CDS code clean up:
>>>>
>>>> Currently all entries in the SymbolTable/StringTable are dumped into
>>>> the CDS archive. The problems are
>>>>
>>>> (1) We end up writing many unused items, such as the mangled names
>>>>     of hidden classes.
>>>> (2) We have to scan the symbol table inside a safepoint, which had
>>>>     caused bugs before (JDK-8245264).
>>>>
>>>> Since JDK-8250990, we already maintain all used Symbols in a growable
>>>> array. We can dump the shared symbol table using this array, and
>>>> avoid walking the SymbolTable.
>>>>
>>>> For StringTable, we scan all archived classes, and dump only the
>>>> interned strings used by those classes (plus extra strings
>>>> specified by SharedArchiveConfigFile) into the CDS interned string
>>>> table.
>>>>
>>>> This reduces complexity in the CDS code, and reduce the size of
>>>> the CDS archives.
>>>>
>>>> Testing - tiers 1-4
>>>>
>>>> Archive file size for "java -Xshare:dump"
>>>>
>>>>    old: 39,368 symbols 7,028 strings 11,784,200 bytes
>>>>    new: 37,387 symbols 7,020 strings 11,683,320 bytes (~0.9% 
>>>> reduction)
>>>>
>>>> Thanks
>>>> - Ioi
>>>>
>>>>
>>
>