Re: [PATCH v6][makedumpfile 00/10] btf/kallsyms based makedumpfile extension for mm page filtering

Hi Kazu,

On Mon, Jun 22, 2026 at 5:57 PM HAGIO KAZUHITO(萩尾　一仁)
<[email protected]> wrote:
>
> Hi Tao,
>
> I've tested some, no issue was detected.
>
> [without the patchset]
> 8.09user 1.01system 0:10.04elapsed 90%CPU (0avgtext+0avgdata 4480maxresident)k
> 18672inputs+763736outputs (0major+268minor)pagefaults 0swaps
>
> [with the patchset without --extension]
> 8.08user 0.99system 0:09.94elapsed 91%CPU (0avgtext+0avgdata 4608maxresident)k  # +128k
> 19640inputs+763720outputs (4major+277minor)pagefaults 0swaps
>
> [with the patchset with --extension]
> 6.38user 0.74system 0:07.92elapsed 89%CPU (0avgtext+0avgdata 16984maxresident)k # +12M
> 17048inputs+725240outputs (0major+3121minor)pagefaults 0swaps
>
> There is also no noticeable rise in max rss without --extension.
>
> Maybe support for compound pages can be debatable in the future, but
> I think the current patchset is good enough for extension v1.
> So merged 01/10 - 09/10 patches, thank you for the great work!

Thanks for your testing, also many thanks for your code review and suggestions!

Thanks,
Tao Liu

>
> Thanks,
> Kazu
>
>
>
> On 2026/06/17 14:18, Tao Liu wrote:
> > A) This patchset will introduce the following features to makedumpfile:
> >
> >    1) Add .so extension support to makedumpfile
> >    2) Enable btf and kallsyms for symbol type and address resolving.
> >
> > B) The purpose of the features are:
> >
> >    1) Currently makedumpfile filters mm pages based on page flags, because flags
> >       can help to determine one page's usage. But this page-flag-checking method
> >       lacks of flexibility in certain cases, e.g. if we want to filter those mm
> >       pages occupied by GPU during vmcore dumping due to:
> >
> >       a) GPU may be taking a large memory and contains sensitive data;
> >       b) GPU mm pages have no relations to kernel crash and useless for vmcore
> >          analysis.
> >
> >       But there is no GPU mm page specific flags, and apparently we don't need
> >       to create one just for kdump use. A programmable filtering tool is more
> >       suitable for such cases. In addition, different GPU vendors may use
> >       different ways for mm pages allocating, programmable filtering is better
> >       than hard coding these GPU specific logics into makedumpfile in this case.
> >
> >    2) Currently makedumpfile already contains a programmable filtering tool, aka
> >       eppic script, which allows user to write customized code for data erasing.
> >       However it has the following drawbacks:
> >
> >       a) cannot do mm page filtering.
> >       b) need to access to debuginfo of both kernel and modules, which is not
> >          applicable in the 2nd kernel.
> >       c) eppic library has memory leaks which are not all resolved [1]. This
> >          is not acceptable in 2nd kernel.
> >
> >       makedumpfile need to resolve the dwarf data from debuginfo, to get symbols
> >       types and addresses. In recent kernel there are dwarf alternatives such
> >       as btf/kallsyms which can be used for this purpose. And btf/kallsyms info
> >       are already packed within vmcore, so we can use it directly.
> >
> >    With these, this patchset introduces makedumpfile extensions, which is based
> >    on btf/kallsyms symbol resolving, and is programmable for mm page filtering.
> >    The following section shows its usage and performance, please note the tests
> >    are performed in 1st kernel.
> >
> >    3) Compile and run makedumpfile extensions:
> >
> >    $ make LINKTYPE=dynamic USELZO=on USESNAPPY=on USEZSTD=on EXTENSION=on
> >    $ make extensions
> >
> >    $ /usr/bin/time -v ./makedumpfile -d 31 -l /var/crash/127.0.0.1-2025-06-10-18\:03\:12/vmcore
> >      /tmp/extension.out --extension amdgpu_filter.so
> >      Loaded extension: ./extensions/amdgpu_filter.so
> >      makedumpfile Completed.
> >          User time (seconds): 5.08
> >          System time (seconds): 0.84
> >          Percent of CPU this job got: 99%
> >          Elapsed (wall clock) time (h:mm:ss or m:ss): 0:05.95
> >          Maximum resident set size (kbytes): 17360
> >          ...
> >
> >       To contrast with eppic script of v2 [2]:
> >
> >    $ /usr/bin/time -v ./makedumpfile -d 31 -l /var/crash/127.0.0.1-2025-06-10-18\:03\:12/vmcore
> >      /tmp/eppic.out --eppic eppic_scripts/filter_amdgpu_mm_pages.c
> >      makedumpfile Completed.
> >          User time (seconds): 8.23
> >          System time (seconds): 0.88
> >          Elapsed (wall clock) time (h:mm:ss or m:ss): 0:09.16
> >          Maximum resident set size (kbytes): 57128
> >          ...
> >
> >    -rw------- 1 root root 367475074 Jan 19 19:01 /tmp/extension.out
> >    -rw------- 1 root root 367475074 Jan 19 19:48 /tmp/eppic.out
> >    -rw------- 1 root root 387181418 Jun 10 18:03 /var/crash/127.0.0.1-2025-06-10-18:03:12/vmcore
> >
> > C) Discussion:
> >
> >    1) GPU types: Currently only tested with amdgpu's mm page filtering, others
> >       are not tested.
> >    2) OS: The code can work on rhel-10+/rhel9.5+ on x86_64/arm64/s390/ppc64.
> >       rhel8.x is not supported, others are not tested.
> >
> > D) Testing:
> >
> >       If you don't want to create your vmcore, you can find a vmcore which I
> >       created with amdgpu mm pages unfiltered [3], the amdgpu mm pages are
> >       allocated by program [4]. You can use the vmcore in 1st kernel to filter
> >       the amdgpu mm pages by the previous performance testing cmdline. To
> >       verify the pages are filtered in crash:
> >
> >       Unfiltered:
> >       crash> search -c "!QAZXSW@#EDC"
> >       ffff96b7fa800000: !QAZXSW@#EDCXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
> >       ffff96b87c800000: !QAZXSW@#EDCXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
> >       crash> rd ffff96b7fa800000
> >       ffff96b7fa800000:  405753585a415121                    !QAZXSW@
> >       crash> rd ffff96b87c800000
> >       ffff96b87c800000:  405753585a415121                    !QAZXSW@
> >
> >       Filtered:
> >       crash> search -c "!QAZXSW@#EDC"
> >       crash> rd ffff96b7fa800000
> >       rd: page excluded: kernel virtual address: ffff96b7fa800000  type: "64-bit KVADDR"
> >       crash> rd ffff96b87c800000
> >       rd: page excluded: kernel virtual address: ffff96b87c800000  type: "64-bit KVADDR"
> >
> > [1]: https://github.com/lucchouina/eppic/pull/32
> > [2]: https://lore.kernel.org/kexec/[email protected]/
> > [3]: https://people.redhat.com/~ltao/core/vmcore
> > [4]: https://gist.github.com/liutgnu/a8cbce1c666452f1530e1410d1f352df
> >
> > v6 -> v5:
> >
> > 1) Add erase_sample extension for data erasure sample.
> > 2) Replace fprintf() to MSG()/ERRMSG() in kallsyms.h.
> > 3) Use handle_cbs_len in extension_has_callback() for callback check.
> > 4) Fix bug[5].
> > 5) Add handle_cbs[i]->cb = NULL in init_extensions() to reset the
> >     callback if one extension's init() is skipped.
> > 6) The patches are organized as follows:
> >
> >     ---- <customization specific> ---
> >     10. Add amdgpu mm pages filtering extension
> >
> >      --- <code should be merged> ---
> >      9. Doc: Add --extension option to makedumpfile manual
> >      8. Add erase_sample extension as an data erase reference
> >      7. Add sample extension as an example reference
> >      6. Add makedumpfile extensions support
> >      5. Implement kernel module's btf resolving
> >      4. Implement kernel module's kallsyms resolving
> >      3. Implement kernel btf resolving
> >      2. Implement kernel kallsyms resolving
> >      1. Reserve sections for makedumpfile and extenions
> >
> >      Patch 10 is customization specific, merging depends on the strategy of
> >      maintenance.
> >      Patch 1 ~ 9 are common code which should be merged with makedumpfile.
> >
> > [5]: https://lore.kernel.org/kexec/[email protected]/
> >
> > Link to v5: https://lore.kernel.org/kexec/[email protected]/
> > Link to v4: https://lore.kernel.org/kexec/[email protected]/
> > Link to v3: https://lore.kernel.org/kexec/[email protected]/
> > Link to v2: https://lore.kernel.org/kexec/[email protected]/
> > Link to v1: https://lore.kernel.org/kexec/[email protected]/
> >
> > Tao Liu (10):
> >    Reserve sections for makedumpfile and extenions
> >    Implement kernel kallsyms resolving
> >    Implement kernel btf resolving
> >    Implement kernel module's kallsyms resolving
> >    Implement kernel module's btf resolving
> >    Add makedumpfile extensions support
> >    Add sample extension as an example reference
> >    Add erase_sample extension as an data erase reference
> >    Doc: Add --extension option to makedumpfile manual
> >    Add amdgpu mm pages filtering extension
> >
> >   Makefile                   |  15 +-
> >   README                     |   6 +
> >   btf_info.c                 | 371 +++++++++++++++++++++++++
> >   btf_info.h                 |  77 ++++++
> >   extension.c                | 355 ++++++++++++++++++++++++
> >   extension.h                |  16 ++
> >   extensions/Makefile        |  13 +
> >   extensions/amdgpu_filter.c | 221 +++++++++++++++
> >   extensions/erase_sample.c  |  78 ++++++
> >   extensions/maple_tree.c    | 328 ++++++++++++++++++++++
> >   extensions/maple_tree.h    |   7 +
> >   extensions/sample.c        |  69 +++++
> >   kallsyms.c                 | 550 +++++++++++++++++++++++++++++++++++++
> >   kallsyms.h                 |  86 ++++++
> >   makedumpfile.8.in          |  11 +-
> >   makedumpfile.c             |  44 ++-
> >   makedumpfile.h             |  12 +
> >   makedumpfile.ld            |  16 ++
> >   18 files changed, 2266 insertions(+), 9 deletions(-)
> >   create mode 100644 btf_info.c
> >   create mode 100644 btf_info.h
> >   create mode 100644 extension.c
> >   create mode 100644 extension.h
> >   create mode 100644 extensions/Makefile
> >   create mode 100644 extensions/amdgpu_filter.c
> >   create mode 100644 extensions/erase_sample.c
> >   create mode 100644 extensions/maple_tree.c
> >   create mode 100644 extensions/maple_tree.h
> >   create mode 100644 extensions/sample.c
> >   create mode 100644 kallsyms.c
> >   create mode 100644 kallsyms.h
> >   create mode 100644 makedumpfile.ld
> >