Integrated: 8263976: Remove block allocation from BasicHashtable

[Coleen Phillimore]

On Mon, 22 Mar 2021 15:49:24 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

> From CR:
> The useful/general BasicHashtable uses a block allocation scheme to reportedly reduce fragmentation. When the StringTable and SymbolTable used to use this hashtable, performance benefits were reportedly observed because of the block allocation scheme. Since these tables were moved to the concurrent hashtables, the tables left that use the block allocation scheme are:
> 
> AdapterHandlerLibrary, ResolutionError, LoaderConstraints, Leak profiler bitset table and Placeholders. 3 of these tables are very small and never needed block allocation to prevent fragmentation at least. Also there are 3 KVHashtables, which are built from BasicHashtable. 2 are used during dumping and 1 is ID2KlassTable which appears small.
> 
> ModuleEntry, PackageEntry, Dictionary, G1RootSet for nmethods, and JvmtiTagMap tables didn't use the block allocation scheme.
> 
> Removing this removes 7 pointers per table, and for each ClassLoaderData, which has 3 tables, removes 21 pointers.
> 
> This change was performance tested on linux and windows.
> 
> It was also tested with tier1-6.

This pull request has now been integrated.

Changeset: 5bc382fb
Author:    Coleen Phillimore <coleenp at openjdk.org>
URL:       https://git.openjdk.java.net/jdk/commit/5bc382fb
Stats:     178 lines in 16 files changed: 10 ins; 131 del; 37 mod

8263976: Remove block allocation from BasicHashtable

Reviewed-by: lfoltan, iklam

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PR: https://git.openjdk.java.net/jdk/pull/3123