8255232: G1: Make G1BiasedMappedArray freeable #808

tschatzl · 2020-10-22T13:47:00Z

Hi all,

can I have reviews for this change that makes G1BiasedMappedArray freeable?

Previously all G1BiasedMappedArray were created as unfreeable i.e. assigned to static variables. However with JDK-8253600 I need one such biased map for the full collector which is created and deleted during full GC. So the biased array should also be freed as necessary to avoid a memory leak.

The alternative would be to statically allocate that map anyway and provide it to the current G1FullCollector instance, but I do not think the single malloc call is perf sensitive compared to full collector work and there is much point in doing something more complicated at this time. In the future I hope that the young gen collector will also be extracted from G1CollectedHeap with the same need. If/when allocation of these helper data structures becomes a problem I would suggest looking into this again.

One option then could be using some ResoureArea for these things in the future.

For this change there should be no change in behavior at all.

Testing: tier1-5

Thanks,
Thomas

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Issue

JDK-8255232: G1: Make G1BiasedMappedArray freeable

Reviewers

Albert Mingkun Yang (@albertnetymk - Author)
Kim Barrett (@kimbarrett - Reviewer)

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$ git fetch https://git.openjdk.java.net/jdk pull/808/head:pull/808
$ git checkout pull/808

bridgekeeper · 2020-10-22T13:47:27Z

👋 Welcome back tschatzl! 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 · 2020-10-22T13:49:44Z

@tschatzl 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 · 2020-10-23T07:18:58Z

Webrevs

01: Full - Incremental (c6835ba)
00: Full (51b297b)

albertnetymk · 2020-10-29T09:00:00Z

src/hotspot/share/gc/g1/g1BiasedArray.cpp

+  if (_alloc_base != NULL) {
+    FREE_C_HEAP_ARRAY(u_char, _alloc_base);
+    _alloc_base = NULL;
+    _base = NULL;
+    _length = 0;
+    _biased_base = NULL;
+    _bias = 0;
+    _shift_by = 0;
+  }


FreeHeap makes more sense to me, since the allocation sites uses AllocateHeap.

Why resetting those fields to zero? The only resource we need to release in this destructor is memory, right?

Will fix.

Some debugging code to see if anyone else is using it after the freeing as previously these tables were never freed - I was not sure if I should keep them or not so I want to see if anyone would complain :) I'll remove these then.

albertnetymk

Thank you for the change.

openjdk · 2020-10-29T12:26:48Z

@tschatzl 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:

8255232: G1: Make G1BiasedMappedArray freeable

Reviewed-by: ayang, kbarrett

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 111 new commits pushed to the master branch:

9e5bbff: 8255550: x86: Assembler::cmpq(Address dst, Register src) encoding is incorrect
5b18558: 8255243: Reinforce escape barrier interactions with ZGC conc stack processing
faf23de: 8255534: Shenandoah: Fix CmpP optimization wrt native-LRB
579e50b: 8255564: InterpreterMacroAssembler::remove_activation() needs to restore thread right after VM call on x86_32
4b20e46: 8255579: x86: Use cmpq(Register,Address) in safepoint_poll
72ff8e2: 8254782: Fix benchmark issues in java/lang/StringIndexOfChar.java benchmark
ea26ff1: 8247614: java/nio/channels/DatagramChannel/Connect.java timed out
38574d5: 8255298: Remove SurvivorAlignmentInBytes functionality
4031cb4: 8254189: Improve comments for StackOverFlow and fix in_xxx() functions
caec8d2: 8233560: [TESTBUG] ToolTipManager/Test6256140.java is failing on macos
... and 101 more: https://git.openjdk.java.net/jdk/compare/ae72b5283b5b5eee0fbb6c9121494a4e65fb381c...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.

tschatzl · 2020-10-29T15:04:55Z

Thanks @albertnetymk @kimbarrett for your reviews.

/integrate

openjdk · 2020-10-29T15:08:28Z

@tschatzl Since your change was applied there have been 111 commits pushed to the master branch:

9e5bbff: 8255550: x86: Assembler::cmpq(Address dst, Register src) encoding is incorrect
5b18558: 8255243: Reinforce escape barrier interactions with ZGC conc stack processing
faf23de: 8255534: Shenandoah: Fix CmpP optimization wrt native-LRB
579e50b: 8255564: InterpreterMacroAssembler::remove_activation() needs to restore thread right after VM call on x86_32
4b20e46: 8255579: x86: Use cmpq(Register,Address) in safepoint_poll
72ff8e2: 8254782: Fix benchmark issues in java/lang/StringIndexOfChar.java benchmark
ea26ff1: 8247614: java/nio/channels/DatagramChannel/Connect.java timed out
38574d5: 8255298: Remove SurvivorAlignmentInBytes functionality
4031cb4: 8254189: Improve comments for StackOverFlow and fix in_xxx() functions
caec8d2: 8233560: [TESTBUG] ToolTipManager/Test6256140.java is failing on macos
... and 101 more: https://git.openjdk.java.net/jdk/compare/ae72b5283b5b5eee0fbb6c9121494a4e65fb381c...master

Your commit was automatically rebased without conflicts.

Pushed as commit 5c520c3.

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

Initial import

51b297b

openjdk bot added the hotspot hotspot-dev@openjdk.org label Oct 22, 2020

tschatzl marked this pull request as ready for review October 23, 2020 07:14

openjdk bot added the rfr Pull request is ready for review label Oct 23, 2020

tschatzl mentioned this pull request Oct 23, 2020

8253600: G1: Fully support pinned regions for full gc #824

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albertnetymk suggested changes Oct 29, 2020

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c6835ba

albertnetymk approved these changes Oct 29, 2020

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openjdk bot added the ready Pull request is ready to be integrated label Oct 29, 2020

openjdk bot closed this Oct 29, 2020

openjdk bot added integrated Pull request has been integrated and removed ready Pull request is ready to be integrated rfr Pull request is ready for review labels Oct 29, 2020

tschatzl deleted the 8255232-freeable-g1biasedmappedarray branch October 29, 2020 15:07

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