RFR: 8250989: Consolidate buffer allocation code for CDS static/dynamic dumping

[Calvin Cheung]

On Thu, 28 Jan 2021 18:14:14 GMT, Ioi Lam <iklam at openjdk.org> wrote:

> Before this PR, when a static CDS archive is dumped, we would unconditionally allocate a 4GB ReservedSpace and use that as the buffer for writing the archive content. We usually don't need such a big ReservedSpace. this also unnecessarily complicates Metaspace::global_initialize().
> 
> After this PR, both we first load all the classes and then allocate a buffer with an appropriate size.
> 
> I also simplified the pointer relocation code that prepares the archive to be mapped at the "requested location" (usually 0x800000000), and improved the comments.
> 
> We used to have lots of special cases for adjusting pointers during dynamic dump. All of those are removed.
> 
> Reviewers, please start with
> - Header comments in archiveBuilder.hpp that describe the overall process of archive dumping
> - `MetaspaceShared::initialize_for_static_dump()`
> - `ArchiveBuilder::reserve_buffer()`
> - Comments around `RelocateBufferToRequested` in archiveBuilder.cpp

The dynamic dumping code is cleaner after this change. Looks good.
I've a few minor comments.

src/hotspot/share/memory/archiveBuilder.cpp line 732:

> 730:   }
> 731:   return buffer_to_offset(p);
> 732: }

Is it possible to add an `assert(DynamicDumpSharedSpaces)` after the `if` statement at line 728?

test/hotspot/jtreg/runtime/cds/appcds/dynamicArchive/DynamicArchiveRelocationTest.java line 96:

> 94:         // (1) Dump base archive (static)
> 95: 
> 96:         OutputAnalyzer out = TestCommon.dumpBaseArchive(baseArchiveName, unlockArg, logArg);

Should the check for `out.shouldContain("Relocating archive from")` be kept?
Otherwise, no need to save the `OutputAnalyzer` returned from `TestCommon.dumpBaseArchive`.

src/hotspot/share/classfile/symbolTable.cpp line 620:

> 618:   OffsetCompactHashtable<const char*, Symbol*, symbol_equals_compact_hashtable_entry> * table;
> 619:   if (is_static_archive) {
> 620:     table = &_shared_table;

Maybe keeping this within a DEBUG_ONLY block if it's still applicable?

-------------

PR: https://git.openjdk.java.net/jdk/pull/2296