8325587: Shenandoah: ShenandoahLock should allow blocking in VM #17813

shipilev · 2024-02-12T17:40:00Z

ShenandoahLock is a spinlock that is supposed to guard heap state. That lock is normally only lightly contended, as threads normally only allocate large TLABs/GCLABs. So we just summarily delegated to Thread::{SpinAcquire,SpinRelease}, which spins a bit, and then starts going to sleep/yield dance on contention.

This does not work well when there are lots of threads near the OOM conditions. Then, most of these threads would fail to allocate the TLAB, go for out-of-TLAB alloc, start lock acquisition, and spend a lot of time trying to acquire the lock. The handshake/safepoint would think those threads are running, even when they are actually yielding or sleeping. As seen in bug report, a handshake operation over many such threads could then take hundreds of seconds.

The solution is to notify VM that we are blocking before going for sleep or yield. This is similar to what other VM code does near such yields. This involves state transitions, so it is only cheap to do near the actual blocking. Protecting the whole lock with VM transition would be very slow.

I also de-uglified bits of adjacent code.

Additional testing:

Original Extremem reproducer does not have outliers anymore
Linux x86_64 server fastdebug, hotspot_gc_shenandoah
Linux x86_64 server fastdebug, all passes with -XX:+UseShenandoahGC (some old failures, but quite a few "timeouts" also disappear)

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Issue

JDK-8325587: Shenandoah: ShenandoahLock should allow blocking in VM (Bug - P3)

Reviewers

Robbin Ehn (@robehn - Reviewer)
Roman Kennke (@rkennke - Reviewer)

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Checkout this PR locally:
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Update a local copy of the PR:
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$ git pull https://git.openjdk.org/jdk.git pull/17813/head

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bridgekeeper · 2024-02-12T17:40:42Z

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openjdk · 2024-02-12T17:41:29Z

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

hotspot-gc
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.

robehn · 2024-02-12T18:39:32Z

Think about if you can add missing pieces to: https://github.com/openjdk/jdk/blob/master/src/hotspot/share/utilities/spinYield.hpp
And utilize that, as it is would be nice to have one? configurable back-off strategy in the future.

Fix Try to block in VM Only enter VM on actual blocking Cleanups Cleanups Only block when in VM state Only block for mutator allocs Simplify

shipilev · 2024-02-13T19:49:33Z

Think about if you can add missing pieces to: https://github.com/openjdk/jdk/blob/master/src/hotspot/share/utilities/spinYield.hpp And utilize that, as it is would be nice to have one? configurable back-off strategy in the future.

Thought about it. The way current patch is done, there is little leeway to make the code common or reuse it, unfortunately.

mlbridge · 2024-02-14T18:30:10Z

Webrevs

01: Full - Incremental (81af0e16)
00: Full (3711cf13)

robehn

I know to little about Shenandoah to say if blocking is always okay, sorry.
Other than that I don't spot any issues, had some minor suggestion.

src/hotspot/share/gc/shenandoah/shenandoahLock.cpp

src/hotspot/share/gc/shenandoah/shenandoahLock.hpp

robehn

Nice work!
I'll review it, but as stated don't trust me that it's works :)

Looks good, thanks!

openjdk · 2024-02-15T12:49:15Z

@shipilev 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:

8325587: Shenandoah: ShenandoahLock should allow blocking in VM

Reviewed-by: rehn, rkennke

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 114 new commits pushed to the master branch:

921507c: 8326319: G1: Remove unused G1ConcurrentMark::_init_times
68eb5a1: 8321075: RISC-V: UseSystemMemoryBarrier lacking proper OS support
04d43c4: 8187759: Background not refreshed when painting over a transparent JFrame
d5f3d5c: 8326201: [S390] Need to bailout cleanly if creation of stubs fails when code cache is out of space
d31fd78: 8325496: Make TrimNativeHeapInterval a product switch
27003b5: 8326090: Rename jvmti_aod.h
36246c9: 8326233: Utils#copySSLParameters loses needClientAuth Setting
14f9aba: 8326371: [BACKOUT] Clean up NativeCompilation.gmk and its newly created parts
1bd91cd: 8325963: Clean up NativeCompilation.gmk and its newly created parts
4d50ee6: 8326368: compare.sh -2bins prints ugly errors on Windows
... and 104 more: https://git.openjdk.org/jdk/compare/618af397b4c636c89049f7398c14f37f0065df59...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.

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rkennke

Looks good. I have one question (and leave it up to you to make the change).

Thanks,
Roman

src/hotspot/share/gc/shenandoah/shenandoahLock.cpp

shipilev · 2024-02-21T11:48:18Z

Thanks!

/integrate

openjdk · 2024-02-21T11:49:01Z

Going to push as commit 492e8bf.
Since your change was applied there have been 115 commits pushed to the master branch:

5f16f34: 8326370: Remove redundant and misplaced micros from StringBuffers
921507c: 8326319: G1: Remove unused G1ConcurrentMark::_init_times
68eb5a1: 8321075: RISC-V: UseSystemMemoryBarrier lacking proper OS support
04d43c4: 8187759: Background not refreshed when painting over a transparent JFrame
d5f3d5c: 8326201: [S390] Need to bailout cleanly if creation of stubs fails when code cache is out of space
d31fd78: 8325496: Make TrimNativeHeapInterval a product switch
27003b5: 8326090: Rename jvmti_aod.h
36246c9: 8326233: Utils#copySSLParameters loses needClientAuth Setting
14f9aba: 8326371: [BACKOUT] Clean up NativeCompilation.gmk and its newly created parts
1bd91cd: 8325963: Clean up NativeCompilation.gmk and its newly created parts
... and 105 more: https://git.openjdk.org/jdk/compare/618af397b4c636c89049f7398c14f37f0065df59...master

Your commit was automatically rebased without conflicts.

openjdk · 2024-02-21T11:49:10Z

@shipilev Pushed as commit 492e8bf.

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

mmyxym · 2024-05-08T11:00:49Z

/backport jdk21u-dev

openjdk · 2024-05-08T11:01:32Z

@mmyxym the backport was successfully created on the branch backport-mmyxym-492e8bf5 in my personal fork of openjdk/jdk21u-dev. To create a pull request with this backport targeting openjdk/jdk21u-dev:master, just click the following link:

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Hi all,

This pull request contains a backport of commit 492e8bf5 from the openjdk/jdk repository.

The commit being backported was authored by Aleksey Shipilev on 21 Feb 2024 and was reviewed by Robbin Ehn and Roman Kennke.

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mmyxym · 2024-05-10T07:26:49Z

/backport jdk22u-dev

openjdk · 2024-05-10T07:27:43Z

@mmyxym The target repository jdk22u-dev is not a valid target for backports.
List of valid target repositories: openjdk/jdk, openjdk/jdk11u, openjdk/jdk11u-dev, openjdk/jdk17u, openjdk/jdk17u-dev, openjdk/jdk21u, openjdk/jdk21u-dev, openjdk/jdk22u, openjdk/jdk7u, openjdk/jdk8u, openjdk/jdk8u-dev, openjdk/jfx, openjdk/jfx17u, openjdk/jfx21u, openjdk/jfx22u, openjdk/lilliput-jdk17u, openjdk/lilliput-jdk21u, openjdk/shenandoah-jdk21u, openjdk/shenandoah-jdk8u.
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mmyxym · 2024-05-10T07:30:48Z

/backport jdk22u

openjdk · 2024-05-10T07:31:42Z

@mmyxym the backport was successfully created on the branch backport-mmyxym-492e8bf5 in my personal fork of openjdk/jdk22u. To create a pull request with this backport targeting openjdk/jdk22u:master, just click the following link:

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Hi all,

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The commit being backported was authored by Aleksey Shipilev on 21 Feb 2024 and was reviewed by Robbin Ehn and Roman Kennke.

Thanks!

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$ git fetch https://github.com/openjdk-bots/jdk22u.git backport-mmyxym-492e8bf5:backport-mmyxym-492e8bf5
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⚠️ @mmyxym You are not yet a collaborator in my fork openjdk-bots/jdk22u. An invite will be sent out and you need to accept it before you can proceed.

shipilev force-pushed the JDK-8325587-shenandoah-lock-yield branch from ab70d4e to 8f9da4f Compare February 12, 2024 17:40

openjdk bot added hotspot-gc hotspot-gc-dev@openjdk.org shenandoah shenandoah-dev@openjdk.org labels Feb 12, 2024

Fix

42bcbe8

Fix Try to block in VM Only enter VM on actual blocking Cleanups Cleanups Only block when in VM state Only block for mutator allocs Simplify

shipilev force-pushed the JDK-8325587-shenandoah-lock-yield branch from fbd242a to 42bcbe8 Compare February 13, 2024 09:58

Touchups

3711cf1

shipilev marked this pull request as ready for review February 14, 2024 18:26

openjdk bot added the rfr Pull request is ready for review label Feb 14, 2024

robehn reviewed Feb 14, 2024

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robehn approved these changes Feb 15, 2024

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openjdk bot added the ready Pull request is ready to be integrated label Feb 15, 2024

rkennke approved these changes Feb 21, 2024

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src/hotspot/share/gc/shenandoah/shenandoahLock.cpp Show resolved Hide resolved

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openjdk bot closed this Feb 21, 2024

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shipilev deleted the JDK-8325587-shenandoah-lock-yield branch March 1, 2024 12:15

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8325587: Shenandoah: ShenandoahLock should allow blocking in VM #17813

8325587: Shenandoah: ShenandoahLock should allow blocking in VM #17813

shipilev commented Feb 12, 2024 •

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8325587: Shenandoah: ShenandoahLock should allow blocking in VM #17813

8325587: Shenandoah: ShenandoahLock should allow blocking in VM #17813

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