JDK-8310388: Shenandoah: Auxiliary bitmap is not madvised for THP #14953

tstuefe · 2023-07-20T11:19:53Z

See details in JBS isse.

Note that there is no actual functional difference. AUX bitmap did not use THPs before this patch and does not now either. The only difference is that before, the JVM thought the AUX bitmap uses THPs when in fact it did not. That caused confusion.

(All this illuminates how badly thought out the ReservedSpace API really is. We pass in page size to the constructor, but then need to commit manually; THPs actually use madvise on commit, not on reservation, so we need to pass page size in again to commit. Ideally, ReservedSpace should handle committing for us with the page size it saved from reservation.)

Note that this only takes care of preventing THP formation in "madvise" mode. In "always" mode, the kernel will do THP coalescation always. We could prevent it from doing so by advising against it via madvise, but that would require extension of the platform generic reservation APIs and is left for a different RFE. Ideally, nobody should use THP "always" mode.

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Issue

JDK-8310388: Shenandoah: Auxiliary bitmap is not madvised for THP (Bug - P4)

Reviewers

Aleksey Shipilev (@shipilev - Reviewer)
Kelvin Nilsen (@kdnilsen - no project role)

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Checkout this PR locally:
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$ git checkout pull/14953

Update a local copy of the PR:
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$ git pull https://git.openjdk.org/jdk.git pull/14953/head

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$ git pr checkout 14953

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bridgekeeper · 2023-07-20T11:20:58Z

👋 Welcome back stuefe! 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 · 2023-07-20T11:23:13Z

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

hotspot
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 · 2023-07-20T15:24:57Z

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01: Full - Incremental (5bc2b246)
00: Full (03ff47b3)

shipilev

Looks fine.

Does it make sense to enable runtime/os/TestTracePageSizes.java now?

shipilev · 2023-07-20T15:39:27Z

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

+  // Note: on Linux, in THP "advise" mode, we refrain from advising the system to use large pages
+  //  since we know these commits will be short lived.
+  const size_t aux_bitmap_page_size =
+    LINUX_ONLY(UseTransparentHugePages ? os::vm_page_size() :) bitmap_page_size;


There is a ifdef LINUX THP-related block in the same file, so better to match its style:

size_t aux_bitmap_page_size = bitmap_page_size; #ifdef LINUX // In THP "advise" mode, we refrain from advising the system to use large pages // since we know these commits will be short lived, and there is no reason to trash // the THP area with this bitmap. if (UseTransparentHugePages) { aux_bitmap_page_size = os::vm_page_size(); } #endif

openjdk · 2023-07-20T15:41:53Z

@tstuefe 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:

8310388: Shenandoah: Auxiliary bitmap is not madvised for THP

Reviewed-by: shade, kdnilsen

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 155 new commits pushed to the master branch:

f66cd50: 8313564: Fix -Wconversion warnings in classfile code
e8a37b9: 8313248: C2: setScopedValueCache intrinsic exposes nullptr pre-values to store barriers
29f1d8e: 8313707: GHA: Bootstrap sysroots with --variant=minbase
61c58fd: 8312976: MatchResult produces StringIndexOutOfBoundsException for groups outside match
5d23295: 8313251: Add NativeLibraryLoad event
c4b8574: 8311938: Add default cups include location for configure on AIX
10a2605: 8294979: test/jdk/tools/jlink 3 test classes use ASM library
e8c325d: 8313394: Array Elements in OldObjectSample event has the incorrect description
d60352e: 8311006: missing @SInCE info in jdk.xml.dom
4577147: 8313712: [BACKOUT] 8313632: ciEnv::dump_replay_data use fclose
... and 145 more: https://git.openjdk.org/jdk/compare/32833285bf94a17989db9bdfa86f58777ab9187d...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.

tstuefe · 2023-07-20T16:19:45Z

Looks fine.

Does it make sense to enable runtime/os/TestTracePageSizes.java now?

Maybe. Possibly. I just found another bug [1] in TestTracePageSizes where it does not correctly identify VMAs that are clearly backed by THPs, because it looks for the VM_xxx flags alone. I rather leave that test out for now to stabilize it a bit more; I don't want to start whacking the mole again.

[1] https://bugs.openjdk.org/browse/JDK-8312471

tstuefe · 2023-08-04T16:05:12Z

Friendly ping... still need a second review.

kdnilsen

Looks good to me.

tstuefe · 2023-08-04T18:39:46Z

Thanks Kelvin!

/integrate

openjdk · 2023-08-04T18:40:19Z

Going to push as commit 017e0c7.
Since your change was applied there have been 155 commits pushed to the master branch:

f66cd50: 8313564: Fix -Wconversion warnings in classfile code
e8a37b9: 8313248: C2: setScopedValueCache intrinsic exposes nullptr pre-values to store barriers
29f1d8e: 8313707: GHA: Bootstrap sysroots with --variant=minbase
61c58fd: 8312976: MatchResult produces StringIndexOutOfBoundsException for groups outside match
5d23295: 8313251: Add NativeLibraryLoad event
c4b8574: 8311938: Add default cups include location for configure on AIX
10a2605: 8294979: test/jdk/tools/jlink 3 test classes use ASM library
e8c325d: 8313394: Array Elements in OldObjectSample event has the incorrect description
d60352e: 8311006: missing @SInCE info in jdk.xml.dom
4577147: 8313712: [BACKOUT] 8313632: ciEnv::dump_replay_data use fclose
... and 145 more: https://git.openjdk.org/jdk/compare/32833285bf94a17989db9bdfa86f58777ab9187d...master

Your commit was automatically rebased without conflicts.

openjdk · 2023-08-04T18:40:30Z

@tstuefe Pushed as commit 017e0c7.

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

openjdk bot added hotspot hotspot-dev@openjdk.org shenandoah shenandoah-dev@openjdk.org labels Jul 20, 2023

tstuefe force-pushed the JDK-8310388-Shenandoah-Auxiliary-bitmap-is-not-madvised-for-THP branch 2 times, most recently from a527256 to ef02c1e Compare July 20, 2023 15:16

JDK-8310388-Shenandoah-Auxiliary-bitmap-is-not-madvised-for-THP

03ff47b

tstuefe force-pushed the JDK-8310388-Shenandoah-Auxiliary-bitmap-is-not-madvised-for-THP branch from ef02c1e to 03ff47b Compare July 20, 2023 15:17

tstuefe marked this pull request as ready for review July 20, 2023 15:19

openjdk bot added the rfr Pull request is ready for review label Jul 20, 2023

shipilev approved these changes Jul 20, 2023

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openjdk bot added the ready Pull request is ready to be integrated label Jul 20, 2023

Alekseys feedback

5bc2b24

shipilev approved these changes Jul 20, 2023

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kdnilsen approved these changes Aug 4, 2023

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JDK-8310388: Shenandoah: Auxiliary bitmap is not madvised for THP #14953

JDK-8310388: Shenandoah: Auxiliary bitmap is not madvised for THP #14953

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JDK-8310388: Shenandoah: Auxiliary bitmap is not madvised for THP #14953

JDK-8310388: Shenandoah: Auxiliary bitmap is not madvised for THP #14953

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