8301992: Embed SymbolTable CHT node #12562

calvinccheung · 2023-02-14T17:29:41Z

Please review this patch for embedding the Symbol inside a ConcurrentHashTable Node instead of having a pointer to a Symbol. This eliminates malloc/free for each Symbol.

This patch is co-authored by @robehn.

Passed tiers 1 - 4 testing.

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Issue

JDK-8301992: Embed SymbolTable CHT node

Reviewers

Coleen Phillimore (@coleenp - Reviewer) ⚠️ Review applies to b22eb3b0
Ioi Lam (@iklam - Reviewer)

Contributors

Robbin Ehn <rehn@openjdk.org>

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk pull/12562/head:pull/12562
$ git checkout pull/12562

Update a local copy of the PR:
$ git checkout pull/12562
$ git pull https://git.openjdk.org/jdk pull/12562/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 12562

View PR using the GUI difftool:
$ git pr show -t 12562

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/12562.diff

bridgekeeper · 2023-02-14T17:30:47Z

👋 Welcome back ccheung! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

calvinccheung · 2023-02-14T17:31:58Z

/contributor add @robehn

openjdk · 2023-02-14T17:32:46Z

@calvinccheung
Contributor Robbin Ehn <rehn@openjdk.org> successfully added.

openjdk · 2023-02-14T17:34:37Z

@calvinccheung The following label will be automatically applied to this pull request:

hotspot

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing list. If you would like to change these labels, use the /label pull request command.

mlbridge · 2023-02-14T17:38:33Z

Webrevs

coleenp

This looks good - I have just a couple of changes that I think you should make.

src/hotspot/share/classfile/symbolTable.cpp

src/hotspot/share/oops/symbol.cpp

src/hotspot/share/classfile/symbolTable.cpp

robehn · 2023-02-15T08:42:30Z

@calvinccheung thanks!

coleenp

This changes look great! thank you!

openjdk · 2023-02-15T22:55:16Z

@calvinccheung This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8301992: Embed SymbolTable CHT node

Co-authored-by: Robbin Ehn <rehn@openjdk.org>
Reviewed-by: coleenp, iklam

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 154 new commits pushed to the master branch:

a917fb3: 7033677: potential cast error in MemberEnter
6120319: 8302226: failure_handler native.core should wait for coredump to finish
fef3eab: 8302734: Parallel: Remove unused LGRPSpace::_invalid_region
ea5bfea: 8302661: Parallel: Remove PSVirtualSpace::is_aligned
edf238b: 8302635: Race condition in HttpBodySubscriberWrapper when cancelling request
cd77fcf: 8290822: C2: assert in PhaseIdealLoop::do_unroll() is subject to undefined behavior
57c9bc3: 8302335: IGV: Bytecode not showing
57fde75: 8302113: Improve CRC32 intrinsic with crypto pmull on AArch64
b8c9d6c: 8302158: PPC: test/jdk/jdk/internal/vm/Continuation/Fuzz.java: AssertionError: res: false shouldPin: false
dc55a7f: 8302202: Incorrect desugaring of null-allowed nested patterns
... and 144 more: https://git.openjdk.org/jdk/compare/2a579ab8392d30a35f044954178c788d16d4b800...master

As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

➡️ To integrate this PR with the above commit message to the master branch, type /integrate in a new comment.

src/hotspot/share/classfile/symbolTable.cpp

coleenp

This seems fine. I haven't actually observed us getting to this code, except maybe once, but you might as well keep it.

iklam · 2023-02-16T18:53:17Z

src/hotspot/share/classfile/symbolTable.cpp

+    if (value.refcount() != PERM_REFCOUNT) {
+      FreeHeap(memory);
+    } else {
+      MutexLocker ml(SymbolArena_lock, Mutex::_no_safepoint_check_flag); // Protect arena
+      // Deleting permanent symbol should not occur very often (insert race condition),
+      // so log it.
+      log_trace_symboltable_helper(&value, "Freeing permanent symbol");
+      size_t alloc_size = _local_table->get_node_size() + value.byte_size() + value.effective_length();
+      if (!SymbolTable::arena()->Afree(memory, alloc_size)) {
+        log_trace_symboltable_helper(&value, "Leaked permanent symbol");
+      }


We should avoid freeing if DumpSharedSpaces is true, so that the code is symmetrical with allocate_node_impl(). Maybe this:

#if INCLUDE_CDS if (DumpSharedSpaces) { // no deallocation is needed } else #endif if (value.refcount() != PERM_REFCOUNT) {

How about performing the above check at the beginning of the function, right after the assert statement as follows?
Let me know if the added assert is necessary.

--- a/src/hotspot/share/classfile/symbolTable.cpp +++ b/src/hotspot/share/classfile/symbolTable.cpp @@ -151,6 +151,13 @@ public: // If #2, then the symbol is dead (refcount==0) assert(value.is_permanent() || (value.refcount() == 1) || (value.refcount() == 0), "refcount %d", value.refcount()); +#if INCLUDE_CDS + if (DumpSharedSpaces) { + assert(value.is_permanent(), "symbol should be permanent during CDS dumping"); + // no deallocation is needed + return; + } +#endif if (value.refcount() == 1) { value.decrement_refcount(); assert(value.refcount() == 0, "expected dead symbol");

Currently, in allocate_node_impl() there's no guarantee that the refcount is always permanent when DumpSharedSpaces is true.

During CDS dumping, some classes may be loaded by non-boot loaders, and their symbols may initially have a non-permanent count. Eventually, we force all the archived symbols to be permanent, but theoretically calls to free_node() may happen before that.

Ok. I've pushed a commit without the assert statement.

iklam

LGTM

calvinccheung · 2023-02-17T19:18:41Z

Thanks @coleenp, @iklam for the review!

/integrate

openjdk · 2023-02-17T19:51:47Z

Going to push as commit 86b9fce.
Since your change was applied there have been 156 commits pushed to the master branch:

03d613b: 8294402: Add diagnostic logging to VMProps.checkDockerSupport
a263f28: 8302777: CDS should not relocate heap if mapping fails
a917fb3: 7033677: potential cast error in MemberEnter
6120319: 8302226: failure_handler native.core should wait for coredump to finish
fef3eab: 8302734: Parallel: Remove unused LGRPSpace::_invalid_region
ea5bfea: 8302661: Parallel: Remove PSVirtualSpace::is_aligned
edf238b: 8302635: Race condition in HttpBodySubscriberWrapper when cancelling request
cd77fcf: 8290822: C2: assert in PhaseIdealLoop::do_unroll() is subject to undefined behavior
57c9bc3: 8302335: IGV: Bytecode not showing
57fde75: 8302113: Improve CRC32 intrinsic with crypto pmull on AArch64
... and 146 more: https://git.openjdk.org/jdk/compare/2a579ab8392d30a35f044954178c788d16d4b800...master

Your commit was automatically rebased without conflicts.

openjdk · 2023-02-17T19:52:55Z

@calvinccheung Pushed as commit 86b9fce.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.

8301992: Embed SymbolTable CHT node

5c7a584

openjdk bot added the rfr Pull request is ready for review label Feb 14, 2023

openjdk bot added the hotspot hotspot-dev@openjdk.org label Feb 14, 2023

coleenp suggested changes Feb 15, 2023

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src/hotspot/share/oops/symbol.cpp Show resolved Hide resolved

iklam suggested changes Feb 15, 2023

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calvinccheung added 2 commits February 15, 2023 17:43

@coleenp and @iklam comments

f7a7812

remove unused allocate_symbol() declaration in symbolTable.hpp

9b4c63d

coleenp approved these changes Feb 15, 2023

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iklam reviewed Feb 15, 2023

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src/hotspot/share/classfile/symbolTable.cpp Show resolved Hide resolved

add Afree() for permanent symbols

b22eb3b

coleenp approved these changes Feb 16, 2023

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iklam reviewed Feb 16, 2023

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do nothing in free_node() if DumpSharedSpaces

0f1d5a8

iklam approved these changes Feb 17, 2023

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openjdk bot added the integrated Pull request has been integrated label Feb 17, 2023

openjdk bot closed this Feb 17, 2023

openjdk bot removed ready Pull request is ready to be integrated rfr Pull request is ready for review labels Feb 17, 2023

8301992: Embed SymbolTable CHT node #12562

8301992: Embed SymbolTable CHT node #12562

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