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

[Ioi Lam]

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

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?
>
> 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"
>
>
> 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
>>>
>>>
>