Re: [PATCH makedumpfile 0/9] Improvements to makedumpfile extensions, plus userspace stack tracing extension

Hi Stephen,

On Tue, Aug 4, 2026 at 4:14=E2=80=AFAM Stephen Brennan
<[email protected]> wrote:
>
> Hello all,
>
> Just a gentle ping on this series.

Sorry I was busy recently due to some internal team issues. Anyway I
will review the patchset, it's on my queue.

Thanks,
Tao Liu

>
> Thanks,
> Stephen
>
> Stephen Brennan <[email protected]> writes:
> > Hello all,
> >
> > Building on Tao Liu's excellent work for makedumpfile extensions, I'd l=
ike to
> > share some incremental improvements to the extension system, as well as=
 my own
> > two extensions which enable userspace stack tracing. There are three to=
pics
> > related to the core makedumpfile extension system which are addressed h=
ere:
> >
> > 1. Tail pages handling. As patch 1 explains, extensions currently get c=
alled for
> > tail pages, but their decisions are not respected. I believe the best a=
pproach
> > is to only call extensions for the head page, but allow extensions to r=
eturn a
> > decision related to just a subset of the pages. To this end, patch 7 ad=
ds
> > PG_INCLUDE_HEAD to include just the head page (leaving the rest up to t=
he
> > default policy), and patch 9 shows the elfheader extension which uses t=
hat
> > functionality.
> >
> > 2. Counting pages included by extensions. This is done by patch 4. It a=
lters the
> > logic because it's really helpful to know whether a page would have bee=
n
> > included by makedumpfile's dump-level filtering anyway, so we only coun=
t the
> > additional pages.
> >
> > 3. Sharing makedumpfile's logic and knowledge about page metadata. Curr=
ently,
> > extensions just get a "pcache" pointer, which means they must redo what=
ever
> > logic makedumpfile has already done, in order to get information like
> > compound_order. Patches 3, 5, and 6 factor out the page metadata into a=
 new
> > struct pginfo, which gets passed to extensions, and it also makes more =
of the
> > helpers like "isSlab()" usable with this pointer.
> >
> > With those improvements, the final two patches (8 & 9) implement a pair=
 of
> > extensions that are useful for including a minimal amount of informatio=
n which
> > can be used to do stack traces of the userspace processes in a vmcore. =
The
> > "userstack" extension includes the stack memory itself for each thread,=
 and the
> > "elfheader" extension includes the first page of mapped ELF files, so t=
hat ELF
> > build IDs can be identified from the vmcore.
> >
> > My testing so far:
> > - Live testing (/proc/kcore) x86_64 on Oracle UEK 8 (6.12.x based)
> > - Refiltering on vmcores generated from UEK8, 7 (5.15.x based), 6 (5.4.=
x based)
> > - Using the resulting filtered vmcores with drgn's contrib/pstack.py to=
 generate
> >   userspace stack traces.
> >
> > I still have significantly more testing to do and then share out:
> > - Testing in kexec environment
> > - Testing with upstream kernels, also verifying in a Fedora userspace
> > - Sharing runtime and size comparisons with different workloads
> >
> > Despite the limited testing, I wanted to share these patches as they ar=
e,
> > because I think the improvements for the core extensions framework are =
useful
> > already, and don't require as much verification.
> >
> > For the extensions themselves, I would like to consider merging them as=
 well, if
> > there is interest. I think it would be useful for makedumpfile to conta=
in shared
> > extensions, including those for the GPU buffers which Tao Liu was worki=
ng on, as
> > well as the userspace stack tracing ones which I'm sharing.
> >
> > Thanks,
> > Stephen
> >
> > Stephen Brennan (9):
> >   Do not call extensions for tail pages
> >   Honor CFLAGS in extension/Makefile
> >   Share page information with extension callbacks
> >   Introduce a stat for pages retained by extension
> >   Move page checks into makedumpfile.h
> >   Simplify arguments for page checks
> >   Add PG_INCLUDE_HEAD extension return status
> >   Add userstack extension
> >   Add elfheader extension
> >
> >  extension.c             |  10 +-
> >  extension.h             |  10 +-
> >  extensions/Makefile     |   8 +-
> >  extensions/elfheader.c  |  93 ++++++++++++
> >  extensions/userstack.c  | 325 ++++++++++++++++++++++++++++++++++++++++
> >  extensions/vma_mtree.c  | 140 +++++++++++++++++
> >  extensions/vma_mtree.h  |   7 +
> >  extensions/vma_rbtree.c |  56 +++++++
> >  extensions/vma_rbtree.h |  12 ++
> >  makedumpfile.c          | 188 +++++++++--------------
> >  makedumpfile.h          |  78 +++++++++-
> >  11 files changed, 798 insertions(+), 129 deletions(-)
> >  create mode 100644 extensions/elfheader.c
> >  create mode 100644 extensions/userstack.c
> >  create mode 100644 extensions/vma_mtree.c
> >  create mode 100644 extensions/vma_mtree.h
> >  create mode 100644 extensions/vma_rbtree.c
> >  create mode 100644 extensions/vma_rbtree.h
> >
> > --
> > 2.47.3
>