8256072: Eliminate JVMTI tagmap rehashing #10938

coleenp · 2022-11-01T22:31:03Z

Use identity_hash for objects in the JVMTI TagMap table. If the object has no hashcode, it's not in the table.
Tested with tier1-6.

Progress

Change must be properly reviewed (1 review required, with at least 1 Reviewer)
Change must not contain extraneous whitespace
Commit message must refer to an issue

Issue

JDK-8256072: Eliminate JVMTI tagmap rehashing

Reviewers

Kim Barrett (@kimbarrett - Reviewer) ⚠️ Review applies to 8770d38c
Erik Österlund (@fisk - Reviewer) ⚠️ Review applies to 8770d38c

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk pull/10938/head:pull/10938
$ git checkout pull/10938

Update a local copy of the PR:
$ git checkout pull/10938
$ git pull https://git.openjdk.org/jdk pull/10938/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 10938

View PR using the GUI difftool:
$ git pr show -t 10938

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/10938.diff

bridgekeeper · 2022-11-01T22:32:49Z

👋 Welcome back coleenp! 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.

openjdk · 2022-11-01T22:36:10Z

@coleenp The following labels will be automatically applied to this pull request:

hotspot
serviceability
shenandoah

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

mlbridge · 2022-11-02T16:47:00Z

Webrevs

coleenp · 2022-11-02T17:04:33Z

/test

kimbarrett

Looks good. Yay code deletion!

I was particularly happy to see set_needs_rehashing removed from all the GCs.

As a followup, I think CollectedHeap::hash_oop is unused after this change.

openjdk · 2022-11-02T20:54:57Z

@coleenp 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:

8256072: Eliminate JVMTI tagmap rehashing

Reviewed-by: kbarrett, eosterlund

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 16 new commits pushed to the master branch:

4338f52: 8294241: Deprecate URL public constructors
68209ad: 8288232: Address typos in jar man page
2ff9d3a: 8294858: XMLStreamReader does not respect jdk.xml.maxXMLNameLimit=0 for namespace names
72f74df: 8292427: Improve specification of InflaterInputStream.fill()
53905e6: 8178355: IdentityHashMap uses identity-based comparison for values everywhere except remove(K,V) and replace(K,V,V)
25dfcbd: 8289689: (fs) Re-examine the need for normalization to Unicode Normalization Format D (macOS)
b7442d1: 8295653: Add a graph of the sealed class hierarchy for marked classes
59a13b1: 8295872: [PPC64] JfrGetCallTrace: Need pc == nullptr check before frame constructor
2a79dfc: 8295774: Write a test to verify List sends ItemEvent/ActionEvent
cc3c5a1: 8296101: nmethod::is_unloading result unstable with concurrent unloading
... and 6 more: https://git.openjdk.org/jdk/compare/c7b95a895fe66a00c754b590ebde53087f183c51...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.

coleenp · 2022-11-02T22:22:19Z

Thanks for the code review Kim. I removed the function that you noticed is now unused.

kimbarrett

Looks good. Maybe just a little more deletion.

kimbarrett · 2022-11-03T03:41:26Z

src/hotspot/share/gc/z/zHeap.inline.hpp


-inline uint32_t ZHeap::hash_oop(uintptr_t addr) const {
-  const uintptr_t offset = ZAddress::offset(addr);
-  return ZHash::address_to_uint32(offset);


I think removal of the call to ZHash::address_to_uint32 means this file no longer needs to include zHash.inline.hpp.

I think you are right Kim.

fisk

I love the use of identity hash code instead of address bits. There might be an issue with displaced markWords though where we need to be careful.

fisk · 2022-11-03T05:28:23Z

src/hotspot/share/prims/jvmtiTagMapTable.cpp

 }

 JvmtiTagMapEntry* JvmtiTagMapTable::find(oop obj) {
+  if (obj->has_no_hash()) {


This new function you added checks if the markWord has a hashCode. If there is a displaced markWord, then it very well might be that there is a hashCode, but it is in the displaced markWord - either in a stack lock or an ObjectMonitor. Bailing here does not seem correct, as it might actually be in the table even if there is no hashCode in the markWord. Is this an optimization?

It is an optimization. I don't think we want to create an identity hash for all oops just for lookup. Is there a better way to find if an oop hashCode?

I was hoping there was just a bit but you're right. I renamed it to fast_no_hash_check() and only return true if the object is unlocked and added a comment.

I'm rerunning jvmti and jdi tests locally.

fisk

Looks good now to me!

coleenp · 2022-11-03T13:51:31Z

Thanks Erik and Kim for reviewing!

kimbarrett

Good thing Erik caught the displaced markword issue. Looks even better now.

kimbarrett · 2022-11-03T17:14:39Z

src/hotspot/share/oops/oop.hpp


  // identity hash; returns the identity hash key (computes it if necessary)
-  inline bool has_no_hash();
+  inline bool fast_no_hash_check();


Seems like fast_no_hash_check ought to be later in this grouping. The preceding comment is about identity_hash.

Ok, this makes sense. Thanks.

coleenp · 2022-11-03T17:25:36Z

Thanks for the re-review Kim. Recompiled with the trivial change.
/integrate

openjdk · 2022-11-03T17:27:13Z

Going to push as commit 94eb25a.
Since your change was applied there have been 16 commits pushed to the master branch:

4338f52: 8294241: Deprecate URL public constructors
68209ad: 8288232: Address typos in jar man page
2ff9d3a: 8294858: XMLStreamReader does not respect jdk.xml.maxXMLNameLimit=0 for namespace names
72f74df: 8292427: Improve specification of InflaterInputStream.fill()
53905e6: 8178355: IdentityHashMap uses identity-based comparison for values everywhere except remove(K,V) and replace(K,V,V)
25dfcbd: 8289689: (fs) Re-examine the need for normalization to Unicode Normalization Format D (macOS)
b7442d1: 8295653: Add a graph of the sealed class hierarchy for marked classes
59a13b1: 8295872: [PPC64] JfrGetCallTrace: Need pc == nullptr check before frame constructor
2a79dfc: 8295774: Write a test to verify List sends ItemEvent/ActionEvent
cc3c5a1: 8296101: nmethod::is_unloading result unstable with concurrent unloading
... and 6 more: https://git.openjdk.org/jdk/compare/c7b95a895fe66a00c754b590ebde53087f183c51...master

Your commit was automatically rebased without conflicts.

openjdk · 2022-11-03T17:27:36Z

@coleenp Pushed as commit 94eb25a.

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

8256072: Eliminate JVMTI tagmap rehashing

29fb0c2

openjdk bot added serviceability serviceability-dev@openjdk.org hotspot hotspot-dev@openjdk.org shenandoah shenandoah-dev@openjdk.org labels Nov 1, 2022

coleenp marked this pull request as ready for review November 2, 2022 16:41

openjdk bot added the rfr Pull request is ready for review label Nov 2, 2022

Merge branch 'master' into jvmti

e549dcb

kimbarrett approved these changes Nov 2, 2022

View reviewed changes

openjdk bot added the ready Pull request is ready to be integrated label Nov 2, 2022

Remove now-unused function that I missed.

f214791

kimbarrett approved these changes Nov 3, 2022

View reviewed changes

fisk suggested changes Nov 3, 2022

View reviewed changes

Fix has_no_hash into fast_no_hash_check().

8770d38

fisk approved these changes Nov 3, 2022

View reviewed changes

kimbarrett approved these changes Nov 3, 2022

View reviewed changes

Fix has_no_hash into fast_no_hash_check().

7bda861

openjdk bot added the integrated Pull request has been integrated label Nov 3, 2022

openjdk bot closed this Nov 3, 2022

openjdk bot removed ready Pull request is ready to be integrated rfr Pull request is ready for review labels Nov 3, 2022

coleenp deleted the jvmti branch November 3, 2022 17:27

8256072: Eliminate JVMTI tagmap rehashing #10938

8256072: Eliminate JVMTI tagmap rehashing #10938

Uh oh!

Conversation

coleenp commented Nov 1, 2022 • edited by openjdk bot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Progress

Issue

Reviewers

Reviewing

Uh oh!

bridgekeeper bot commented Nov 1, 2022

Uh oh!

openjdk bot commented Nov 1, 2022

Uh oh!

mlbridge bot commented Nov 2, 2022 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Webrevs

Uh oh!

coleenp commented Nov 2, 2022

Uh oh!

kimbarrett left a comment • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

openjdk bot commented Nov 2, 2022 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

coleenp commented Nov 2, 2022

Uh oh!

kimbarrett left a comment

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

fisk left a comment

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

fisk left a comment

Choose a reason for hiding this comment

Uh oh!

coleenp commented Nov 3, 2022

Uh oh!

kimbarrett left a comment

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

coleenp commented Nov 3, 2022

Uh oh!

openjdk bot commented Nov 3, 2022

Uh oh!

openjdk bot commented Nov 3, 2022

Uh oh!

Reviewers

Assignees

Labels

Milestone

Development

Uh oh!

3 participants

coleenp commented Nov 1, 2022 •

edited by openjdk bot

Loading

mlbridge bot commented Nov 2, 2022 •

edited

Loading

kimbarrett left a comment •

edited

Loading

openjdk bot commented Nov 2, 2022 •

edited

Loading