RFR (S) 8014262 - more footprint info for PrintStringTableStatistics

[Ioi Lam]

Still looking for a reviewer. Advice on C++/template coding style below 
would be really appreciated!

Thanks
- Ioi

On 05/09/2013 11:52 AM, Ioi Lam wrote:
> Please review:
>
> http://cr.openjdk.java.net/~iklam/8014262/table_stats_001/
>
>
> Bug: PrintStringTableStatistics should include more footprint info
>
> http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=8014262
>     https://jbs.oracle.com/bugs/browse/JDK-8014262
>
>
> Summary of fix:
>
>     StringTable and SymbolTable take up significant footprint (about
>     4.5% of total footprint of Eclipse). The old output doesn't has very
>     little info
>
>     ---OLD---
>     Number of buckets       :   20011
>     Average bucket size     :       8
>     Variance of bucket size :       8
>     Std. dev. of bucket size:       3
>     Maximum bucket size     :      25
>     StringTable statistics:
>     Number of buckets       :   60013
>     Average bucket size     :       0
>     Variance of bucket size :       0
>     Std. dev. of bucket size:       1
>     Maximum bucket size     :       6
>
>
>     I modified it to print these:
>
>     ---NEW---
>     SymbolTable statistics:
>     Number of buckets       :     20011 =    160088 bytes, avg    8.00
>     Number of entries       :    166724 =   4001376 bytes, avg   24.00
>     Number of literals      :    166724 =   7943576 bytes, avg   47.65
>     Total footprint         :           =  12105040 bytes
>     Average bucket size     :     8.332
>     Variance of bucket size :     8.308
>     Std. dev. of bucket size:     2.882
>     Maximum bucket size     :        25
>     StringTable statistics:
>     Number of buckets       :     60013 =    480104 bytes, avg    8.00
>     Number of entries       :     25822 =    619728 bytes, avg   24.00
>     Number of literals      :     25822 =   2458696 bytes, avg   95.22
>     Total footprint         :           =   3558528 bytes
>     Average bucket size     :     0.430
>     Variance of bucket size :     0.435
>     Std. dev. of bucket size:     0.659
>     Maximum bucket size     :         6
>
>
> Templave vs virtual function:
>
>     Part of this code is kind of ugly, in hashtable.cpp:
>
>        ...void Hashtable<T, F>::dump( ...) {
>        ...
>            for (HashtableEntry<T, F>* e = table->bucket(i);
>     264       e != NULL; e = e->next()) {
>     265       count++;
>     266       literal_bytes += literal_size(e->literal());
>     267     }
>
>
>     literal_size() is magically matched by the templates to call one 
> of these
>     in hashtable.hpp:
>
>         template <class T, MEMFLAGS F> class Hashtable : public 
> BasicHashtable<F> {
>         ...
>     286   static int literal_size(Symbol *symbol);
>     287   static int literal_size(oop oop);
>     288   static int literal_size(ConstantPool *cp) {Unimplemented(); 
> return 0;} // currently not used
>     289   static int literal_size(Klass *k) {Unimplemented(); return 
> 0;} // currently not used
>
>
>     I am wondering if I should change this to be a virtual function 
> instead.
>     However, none of the current hashtable code uses virtual 
> functions. So it
>     is considered OK to have a virtual function like this:
>
>         template <class T, MEMFLAGS F> class Hashtable : public 
> BasicHashtable<F> {
>           public:
>             virtual int literal_size(T) {return 0;}
>             ...
>         }
>
>         class SymbolTable : public Hashtable<Symbol*, mtSymbol> {
>           public:
>             virtual int literal_size(Symbol* sym) {return sym->size() 
> * HeapWordSize;}
>             ...
>         }
>
>     Any suggestions?
>
> Tests:
>
>     This code path is not taken in regular JVM executions, so
>     I just ran JPRT to make sure the code builds on all platforms.
>
>     Tested manually on Linux and Solaris:
>     $ java -XX:+PrintStringTableStatistics -version
>
>
> Thanks
> - Ioi
>