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Date:      Tue, 13 Feb 2024 07:05:09 +0000
From:      bugzilla-noreply@freebsd.org
To:        fs@FreeBSD.org
Subject:   [Bug 275594] High CPU usage by arc_prune; analysis and fix
Message-ID:  <bug-275594-3630-c9vl443qHL@https.bugs.freebsd.org/bugzilla/>
In-Reply-To: <bug-275594-3630@https.bugs.freebsd.org/bugzilla/>
References:  <bug-275594-3630@https.bugs.freebsd.org/bugzilla/>

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D275594

--- Comment #51 from Seigo Tanimura <seigo.tanimura@gmail.com> ---
(In reply to Seigo Tanimura from comment #44)

The updated fix is now ready to share.

As of writing this, the test on releng/13.2 is running well without any
unexpected build errors.  Hopefully all of the latest fixes are ready for t=
he
review and merge.

* Updates

- Accelerate the ZFS vnode recycling when there are any ARC eviction waiter=
s.
- Recycle the nullfs vnodes, triggered by the vm_lowmem kernel events.


* Github Sources

All of the sources are under
https://github.com/altimeter-130ft/freebsd-freebsd-src.

- Branches and Git Commit Hashes

            |                                                         | Git
Commit Hash
            | Fix Branch                                              |
Base Branch | Fix + Counter Branch                                    | Base
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D+=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D+=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
main        | topic-openzfs-arc_prune-regulation-fix                  |
57ddfad884
            | topic-openzfs-arc_prune-regulation-counters             |=20
------------+---------------------------------------------------------+----=
-------------
stable/14   | stable/14-topic-openzfs-arc_prune-regulation-fix        |
20a6f4779a
            | stable/14-topic-openzfs-arc_prune-regulation-counters   |=20
------------+---------------------------------------------------------+----=
-------------
releng/14.0 | releng/14.0-topic-openzfs-arc_prune-regulation-fix      |
4edf3b8073
            | releng/14.0-topic-openzfs-arc_prune-regulation-counters |=20
------------+---------------------------------------------------------+----=
-------------
stable/13   | stable/13-topic-openzfs-arc_prune-regulation-fix        |
9d2f548bbe
            | stable/13-topic-openzfs-arc_prune-regulation-counters   |=20
------------+---------------------------------------------------------+----=
-------------
releng/13.3 | releng/13.3-topic-openzfs-arc_prune-regulation-fix      |
24eb518714
            | releng/13.3-topic-openzfs-arc_prune-regulation-counters |=20
------------+---------------------------------------------------------+----=
-------------
releng/13.2 | releng/13.2-topic-openzfs-arc_prune-regulation-fix      |
c78c31d2ef
            | releng/13.2-topic-openzfs-arc_prune-regulation-counters |=20

            | Git Commit Hash
            | FreeBSD-EN-23:18.openzfs | ZFS & VFS  | Nullfs     | Counters
Base Branch | Backport                 | Fix        | Fix        | (Not for
merging)
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D+=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D+=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D+=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D+=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D
main        | N/A                      | cb4a97bd6b | 7bbbce6313 | ed4932a2=
b4
------------+--------------------------+------------+------------+---------=
----------
stable/14   | N/A                      | f1e1c524a3 | 69f7866c36 | 4e5471ad=
e7
------------+--------------------------+------------+------------+---------=
----------
releng/14.0 | N/A                      | af25ebd2d0 | d13f4d74a0 | 09103b5f=
9c
------------+--------------------------+------------+------------+---------=
----------
stable/13   | c733dcff2e               | 9c65b44d3d | e2bac2ef1e | d52eb312=
27
------------+--------------------------+------------+------------+---------=
----------
releng/13.3 | ca178f626f               | 90bfaef58d | bd4cceca37 | aad94888=
3e
------------+--------------------------+------------+------------+---------=
----------
releng/13.2 | c733dcff2e               | 9c65b44d3d | e2bac2ef1e | d52eb312=
27


* poudriere-bulk(8) Results

- Contents of Result Chart Archives
  - poudriere-bulk-(base-branch)-(timestamp).7z
    - vnodes.png
      - The overall vnodes.
    - vnode-free-calls.png
      - The calls to the vnode recycle functions.
    - freed-vnodes.png
      - The vnodes freed for recycling.
    - nullfs-nodes.png
      - The nullfs vnodes.
    - vm_lowmem-kernel-events.png
      - The vm_lowmem kernel events.
  - poudriere-bulk-(base-branch)-(timestamp)-zfs.7z
    - zfs-arc-dnode-size.png
      - The ZFS ARC dnode size in bytes.
    - zfs-arc-pruning-regulation.png
      - The ZFS ARC pruning requests and regulation.
    - zfs-znodes-and-dnodes.png
      - The ZFS ARC znodes and dnodes.
    - zfs-dnodes-and-freeing-activity.png
      - The ZFS ARC dnodes and pruning activity.
  - poudriere-bulk-(base-branch)-(timestamp)-zfs-sizes.7z
    - zfs-arc-mru-metadata-size.png
      - The ZFS ARC MRU metadata size.
    - zfs-arc-mru-data-size.png
      - The ZFS ARC MRU data size.
    - zfs-arc-mfu-metadata-size.png
      - The ZFS ARC MFU metadata size.
    - zfs-arc-mfu-data-size.png
      - The ZFS ARC MFU data size.
  - Some charts and traces are not available in 13.x due to the major versi=
on
difference.


- Common Setup
  - sysctl(3)
    - vfs.zfs.arc_max: 4294967296
      - 4GB.
    - vfs.zfs.arc.dnode_limit: 0 (default)
      - kstat.zfs.misc.arcstats.arc_dnode_limit: 322122547 (calculated
automatically)
  - poudriere-bulk(8)
    - USE_TMPFS=3D"wrkdir data localbase"

- releng/14.0

  - Date
    - 09 Feb 2024 00:30Z - 09 Feb 2024 09:07Z
  - Build time
    - 09:06:22 (234 pkgs / hr)

  - Failed port(s): 3
    - japanese/xv: Expected, port Makefile problem?
    - graphics/gimp-app: Expected, a compiler internal error.
    - java/eclipse: Expected, JVM out of heap.
  - Skipped port(s): 2
    - graphics/gimp: graphics/gimp-app.
    - print/gimp-gutenprint: graphics/gimp-app.

  - Result Chart Archive
    - poudriere-bulk-14_0_release_p4-2024-02-09_09h30m00s.7z, Attachment
#248418
    - poudriere-bulk-14_0_release_p4-2024-02-09_09h30m00s-zfs.7z, Attachment
#248419
    - poudriere-bulk-14_0_release_p4-2024-02-09_09h30m00s-zfs-sizes.7z,
Attachment #248420


- releng/13.3

  - Date
    - 08 Feb 2024 03:20Z - 09 Feb 2024 12:01Z
  - Build time
    - 09:00:46 (237 pkgs / hr)

  - Failed port(s): 1
    - japanese/xv: Expected, port Makefile problem?
  - Skipped port(s): 0

  - Result Chart Archive
    - poudriere-bulk-13_3_beta_1-2024-02-08_12h20m00s.7z, Attachment #248421
    - poudriere-bulk-13_3_beta_1-2024-02-08_12h20m00s-zfs.7z, Attachment
#248422
    - poudriere-bulk-13_3_beta_1-2024-02-08_12h20m00s-zfs-sizes.7z, Attachm=
ent
#248423
      - Missing traces
        - The total sizes of each ARC states and types. (Data and metadata)

- releng/13.2

  - In progress.
    - Started at 13 Feb 2024 02:40Z.


- main, stable/14, stable/13

  - No plan for the poudriere-bulk(8) tests for now.
    - stable/14 and stable/13 are expected to behave like releng/14.0 and
releng/13.3, respectively.


- Analysis and Findings

  - The ZFS ARC dnodes stayed at most ~400MB.
    - Before the nullfs fix: monotonic increase in general.
    - The ZFS ARC dnodes decreased when only a few builders were running.
  - The vnodes stayed at most ~1.2M.
    - Before the nullfs fix: up to ~3M.
  - The nullfs node number is controlled well as per the build load.
  - There are often the ARC eviction waiters in the late stage of
poudriere-bulk(8).
    - The tmpfs wrkdirs hold a lot of files for both the build and
prerequisites.
  - There are almost always some ARC-prunable vnodes.
  - The ZFS ARC always have some evictable parts.
    - Almost all data in the ZFS ARC is evictable.

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