8337217: Port VirtualMemoryTracker to use VMATree #20425

afshin-zafari · 2024-08-01T15:44:32Z

VMATree is used instead of SortedLinkList in new class VirtualMemoryTracker.
A wrapper/helper RegionTree is made around VMATree to make some calls easier.
find_reserved_region() is used in 4 cases, it will be removed in further PRs.
All tier1 tests pass except this https://bugs.openjdk.org/browse/JDK-8335167.

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Issue

JDK-8337217: Port VirtualMemoryTracker to use VMATree (Enhancement - P4)

Reviewers

Johan Sjölen (@jdksjolen - Reviewer)
Gerard Ziemski (@gerard-ziemski - Reviewer) Review applies to 815092d2

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk.git pull/20425/head:pull/20425
$ git checkout pull/20425

Update a local copy of the PR:
$ git checkout pull/20425
$ git pull https://git.openjdk.org/jdk.git pull/20425/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 20425

View PR using the GUI difftool:
$ git pr show -t 20425

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/20425.diff

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Link to Webrev Comment

bridgekeeper · 2024-08-01T15:45:21Z

👋 Welcome back azafari! 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 · 2024-08-01T15:45:52Z

@afshin-zafari 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:

8337217: Port VirtualMemoryTracker to use VMATree

Reviewed-by: jsjolen, gziemski

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 1 new commit pushed to the master branch:

5726606: 8359709: java.net.HttpURLConnection sends unexpected "Host" request header in some cases after JDK-8344190

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openjdk · 2024-08-01T15:46:27Z

@afshin-zafari The following labels will be automatically applied to this pull request:

core-libs
hotspot

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.

afshin-zafari · 2024-08-01T16:10:34Z

/label hotspot-runtime

openjdk · 2024-08-01T16:11:45Z

@afshin-zafari
The hotspot-runtime label was successfully added.

jdksjolen

Hi,

Great work! I'm slowly working through the code, let's take our time with this. My PR got too stressful for everyone involved :-/.

I've reviewed some of the code. Could you go a bit more in-depth on what the results of this work was? Did it improve performance, for example?

All tier1 tests pass except one that expects a 50% increase in committed memory but it does not happen.

~~I don't understand what this means, could you expand on this?~~ Edit: Re-read it again now and I get it, which test is this?

Thanks!

src/java.base/share/classes/java/lang/String.java

jdksjolen · 2024-08-02T08:26:53Z

src/hotspot/share/nmt/vmatree.hpp

@@ -37,8 +37,9 @@
 // For example, the state may go from released memory to committed memory,
 // or from committed memory of a certain MEMFLAGS to committed memory of a different MEMFLAGS.
 // The set of points is stored in a balanced binary tree for efficient querying and updating.
-class VMATree {
+class VMATree : public AnyObj {


Why is it AnyObj now?

Mainly to be able to use new operator. Changed to CheapObj<mtNMT>.

test/hotspot/gtest/nmt/test_nmt_treap.cpp

src/hotspot/share/nmt/virtualMemoryTrackerWithTree.cpp

jdksjolen · 2024-08-02T08:41:54Z

src/hotspot/share/nmt/virtualMemoryTrackerWithTree.cpp

+    });
+}
+
+void VirtualMemoryTrackerWithTree::apply_summary_diff(VMATree::SummaryDiff diff) {


Applying a summary diff in the MemoryFileTracker is this:

for (int i = 0; i < mt_number_of_types; i++) { VirtualMemory* summary = file->_summary.by_type(NMTUtil::index_to_flag(i)); summary->reserve_memory(diff.flag[i].commit); summary->commit_memory(diff.flag[i].commit); }

This is much simpler and doesn't require looking at signs and so on.

In MemoryFileTracker, the changes in commit/reserve are applied to a local VirtualMemorySnapshot. Here we have to apply them to the global VirtualMemorySummary.

Yeah, that doesn't seem like a problem.

for (int i = 0; i < mt_number_of_types; i++) { r = diff.flag[i].reserve; c = diff.flag[i].commit; flag = NMTUtil::index_to_flag(i); VirtualMemory* mem = VirtualMemorySummary::as_snapshot()->by_type(flag); reserved = mem->reserved(); committed = mem->committed(); mem->reserve_memory(r); mem->commit_memory(c); if ((size_t)-r > reserved) { print_err("release"); } if ((size_t)-c > reserved || (size_t)c > committed) { print_err("uncommit"); } }

This applies the reserve/commit regardless of outcome, so slightly different.

The main purpose of the if (...) cases is to find if the request to apply the delta is valid or not. There are related assertions in VirtualMemory but not so informative. Also, using log_debug lets the build proceed and just show the messages.
These messages help a lot when something goes wrong in terms of commit/uncommit/release failure.

How does my example code not account for this? You can still get rid of the sign checking.

Case of 'commit' error is missing from your suggestion. At commit time, c > reserved is invalid too.
(size_t)-r for positive r is a large number and is greater than reserved.
We have to find out the intent of the call first (by checking the sign of r or c) and then check if it is valid or not.

test/hotspot/gtest/nmt/test_vmatree.cpp

src/hotspot/share/nmt/regionsTree.hpp

src/hotspot/share/nmt/virtualMemoryTrackerWithTree.hpp

src/hotspot/share/nmt/regionsTree.hpp

src/hotspot/share/nmt/virtualMemoryTrackerWithTree.hpp

afshin-zafari

Thanks for your comments. They are replied or applied.

…-zafari/jdk into _8337217_nmt_VMT_with_tree

openjdk · 2024-08-04T17:54:40Z

⚠️ @afshin-zafari This pull request contains merges that bring in commits not present in the target repository. Since this is not a "merge style" pull request, these changes will be squashed when this pull request in integrated. If this is your intention, then please ignore this message. If you want to preserve the commit structure, you must change the title of this pull request to Merge <project>:<branch> where <project> is the name of another project in the OpenJDK organization (for example Merge jdk:master).

src/hotspot/share/nmt/regionsTree.hpp

src/hotspot/share/nmt/virtualMemoryTrackerWithTree.hpp

jdksjolen · 2024-08-05T08:41:49Z

src/hotspot/share/nmt/virtualMemoryTrackerWithTree.cpp

+    });
+}
+
+void VirtualMemoryTrackerWithTree::apply_summary_diff(VMATree::SummaryDiff diff) {


Yeah, that doesn't seem like a problem.

for (int i = 0; i < mt_number_of_types; i++) { r = diff.flag[i].reserve; c = diff.flag[i].commit; flag = NMTUtil::index_to_flag(i); VirtualMemory* mem = VirtualMemorySummary::as_snapshot()->by_type(flag); reserved = mem->reserved(); committed = mem->committed(); mem->reserve_memory(r); mem->commit_memory(c); if ((size_t)-r > reserved) { print_err("release"); } if ((size_t)-c > reserved || (size_t)c > committed) { print_err("uncommit"); } }

jdksjolen · 2024-08-05T08:42:43Z

src/hotspot/share/nmt/virtualMemoryTrackerWithTree.cpp

+    });
+}
+
+void VirtualMemoryTrackerWithTree::apply_summary_diff(VMATree::SummaryDiff diff) {


This applies the reserve/commit regardless of outcome, so slightly different.

jdksjolen · 2024-08-05T08:44:51Z

src/hotspot/share/nmt/virtualMemoryTrackerWithTree.hpp

+  static RegionsTree* tree() { return _tree; }
+
+ private:
+  static RegionsTree* _tree;


If you do the instance/static pattern then you can switch this into a regular member, no pointer necessary.

The _tree ctor to be called in initialize with a bool depending the NMT_Level. Existing VMT also uses a pointer to a SortedLinkList.
I am not sure yet: What is the advantage of not-a-pointer member? How the instance/static helps this?

src/hotspot/share/nmt/vmatree.hpp

test/hotspot/gtest/nmt/test_nmt_treap.cpp

afshin-zafari

More fixes and questions.

afshin-zafari · 2024-08-07T11:04:57Z

Performance test runs insert/remove operations for SortedLinkList (SLL in the code) and Treap and expects that Treap be faster. Both tests pass with a factor of 70+ faster for 10000 elements.

…mance test compares VMT and VMA.

gerard-ziemski · 2024-08-08T20:58:47Z

Are we keeping both the linked list based and VMATree based implementations just for the review process, and we will drop the linked list one, once we are done with the review, or are they both going to be checked in?

gerard-ziemski · 2024-08-08T21:08:21Z

Is there a concrete advantage here for using lambda expression when iterating committed regions? I'm asking because personally I find

    while ((committed_rgn = itr.next()) != nullptr) {
      print_committed_rgn(committed_rgn);
    }

simpler and more compact, hence easier to understand, than

    CommittedMemoryRegion cmr;
    VirtualMemoryTrackerWithTree::tree()->visit_committed_regions(reserved_rgn, &cmr, [&](CommittedMemoryRegion* crgn) {
      print_committed_rgn(crgn);
      return true;
    });

gerard-ziemski · 2024-08-08T21:10:18Z

Same here:

    if (MemTracker::is_using_tree()) {
      CommittedMemoryRegion cmr;
      bool reserved_and_committed = false;
      VirtualMemoryTrackerWithTree::tree()->visit_committed_regions(reserved_rgn,
                                                                    &cmr,
                                                                    [&](CommittedMemoryRegion* committed_rgn) {
        if (committed_rgn->size() == reserved_rgn->size() && committed_rgn->call_stack()->equals(*stack)) {
          // One region spanning the entire reserved region, with the same stack trace.
          // Don't print this regions because the "reserved and committed" line above
          // already indicates that the region is committed.
          reserved_and_committed = true;
          return false;
        }
        return true;
      });

      if (reserved_and_committed)
        return;
    }
  }

We are setting reserved_and_committed inside lambda, then we need to check it outside. It's messy and harder to follow which return belongs to which context.

src/hotspot/share/nmt/memReporter.cpp

…th_tree

bridgekeeper · 2025-04-04T15:20:45Z

@afshin-zafari This pull request has been inactive for more than 4 weeks and will be automatically closed if another 4 weeks passes without any activity. To avoid this, simply add a new comment to the pull request. Feel free to ask for assistance if you need help with progressing this pull request towards integration!

…th_tree

bridgekeeper · 2025-05-02T19:55:51Z

@afshin-zafari This pull request has been inactive for more than 8 weeks and will now be automatically closed. If you would like to continue working on this pull request in the future, feel free to reopen it! This can be done using the /open pull request command.

…th_tree

afshin-zafari · 2025-06-16T12:01:56Z

/open

openjdk · 2025-06-16T12:02:22Z

@afshin-zafari This pull request is now open

jdksjolen

LGTM!

gerard-ziemski

Small changes (copyright years) and one question, otherwise LGTM.

Nice!

gerard-ziemski · 2025-06-17T15:53:04Z

test/hotspot/gtest/runtime/test_virtualMemoryTracker.cpp

+    RegionsTree* rtree = VirtualMemoryTracker::Instance::tree();
+    rtree->tree().remove_all();


Why are we calling remove_all() right after we create the tree?

We are not creating the tree here. We just retrieve it from the Instance of VMT. Since the tree is also visible to other tests (it is static and not created per test), any changes in other tests will be visible here by this test. This is not as expected in the design of the tests (tests assume that tree is empty at the beginning of the test).

src/hotspot/share/nmt/regionsTree.cpp

src/hotspot/share/nmt/regionsTree.hpp

…th_tree

afshin-zafari · 2025-06-18T11:36:22Z

Thanks for reviews @gerard-ziemski and @jdksjolen.
/integrate

openjdk · 2025-06-18T11:37:48Z

Going to push as commit 547ce03.
Since your change was applied there have been 3 commits pushed to the master branch:

f07f5ce: 8359067: Fix typo in DelayScheduler.java
cabd7c1: 8356897: Update NSS library to 3.111
5726606: 8359709: java.net.HttpURLConnection sends unexpected "Host" request header in some cases after JDK-8344190

Your commit was automatically rebased without conflicts.

openjdk · 2025-06-18T11:37:55Z

@afshin-zafari Pushed as commit 547ce03.

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

wenshao and others added 3 commits July 30, 2024 15:23

handle null argument

33326b0

first tests passed

d044ef7

added performance tests.

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afshin-zafari added 2 commits August 4, 2024 19:39

Merge branch 'openjdk:master' into _8337217_nmt_VMT_with_tree

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Merge branch '_8337217_nmt_VMT_with_tree' of http://github.com/afshin…

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…-zafari/jdk into _8337217_nmt_VMT_with_tree

some fixes and improvements.

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afshin-zafari added 2 commits August 5, 2024 19:41

review comments applied (round 2).

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performance test compares SSL with Treap.

3ed28c2

afshin-zafari added 2 commits August 7, 2024 15:40

some fixes for type casting for builds on other platforms. And perfor…

733fb42

…mance test compares VMT and VMA.

missing type-casts fixed.

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gerard-ziemski suggested changes Aug 8, 2024

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Merge remote-tracking branch 'origin/master' into _8337217_nmt_VMT_wi…

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fixes after merge with master.

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Merge remote-tracking branch 'origin/master' into _8337217_nmt_VMT_wi…

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fixes to a few failures.

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afshin-zafari added 2 commits June 18, 2025 10:58

copyright years

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Merge remote-tracking branch 'origin/master' into _8337217_nmt_VMT_wi…

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		RegionsTree* rtree = VirtualMemoryTracker::Instance::tree();
		rtree->tree().remove_all();

8337217: Port VirtualMemoryTracker to use VMATree #20425

8337217: Port VirtualMemoryTracker to use VMATree #20425

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