[PATCH v9 0/8] kdump: reduce vmcore size and capture time

Tue Nov 10 00:47:35 PST 2026

Hi Wandun,

On Mon, Nov 09, 2026 at 08:23:16PM +0800, Wandun wrote:
> 
> On 10/21/26 16:30, Wandun Chen wrote:
> > From: Wandun Chen <chenwandun at lixiang.com>
> > 
> > On SoCs that carve out large firmware-owned reserved memory (GPU,
> > camera ISP, ...), kdump currently dumps those carveouts as part of
> > system RAM even though their contents are firmware state that is not
> > useful for kernel crash analysis.
> > 
> > ACPI systems already filter reserved memory out of the vmcore through
> > their existing path: firmware reports those carveouts as unusable in
> > the EFI memory map, they get MEMBLOCK_NOMAP set in memblock.memory
> > (is_usable_memory(), efi-init.c), and the ELF header builder has
> > always skipped nomap regions; only DT-based systems currently fail
> > to filter these regions, which is what this series addresses.
> > 
> > This series introduces a MEMBLOCK_NODUMP flag (suggested by Rob) in
> > memblock to filter reserved memory on DT-based architectures. A new
> > flag is needed because MEMBLOCK_NOMAP can only express regions without
> > a linear mapping, while MEMBLOCK_NODUMP can filter regions that are
> > linearly mapped. Reserved regions are marked MEMBLOCK_NODUMP by default
> > so kdump omits them; reusable CMA regions are different because their
> > pages are handed back to the buddy allocator and may carry crash-relevant
> > data.
> > 
> > Since the reserved memory regions are filtered out, the vmcore is
> > smaller in size and faster to produce.
> > 
> > The series is based on linux-next and is organized as follows:
> > 
> > Patches 1-3: Preparation and bugfixes: switch riscv crash_mem to
> >              memblock, fold the duplicated per-arch memblock walks
> >              into the weak defaults, and serialize crash header
> >              preparation against memory hotplug.
> > Patches 4-7: NODUMP infrastructure: switch crash_core to
> >              for_each_mem_region(), introduce the MEMBLOCK_NODUMP
> >              flag, add a dumpable flag to struct reserved_mem, and
> >              mark /reserved-memory entries with MEMBLOCK_NODUMP.
> > Patch 8:     Skip MEMBLOCK_NODUMP regions when building the vmcore
> >              ELF header.
> 
> Hi all,
> 
> A gentle ping on this series.
> 
> I'd appreciate any further feedback, particularly on the
> MEMBLOCK_NODUMP discussion and the issues raised in the Sashiko
> review.

I'm fine with MEMBLOCK_NODUMP.
The issue Sashiko raised about bound check against cmem->max_nr_ranges
seems valid. 

I didn't check the reserved mem one.

> Please let me know if there are any other concerns or suggestions
> before I prepare the next revision.

I believe that should be rebased to account for reserved memory changes.
The riscv change from resources to memblock needs an Ack from riscv
maintainers.

And with all that I can take the next version via kexec tree.

> Thanks,
> Wandun
> 
> > 
> > v8 --> v9:
> > 1. Patch 7: Avoid a potential boot panic on SH when NODUMP marking requires
> >    memblock resizing before it is allowed, found by Sashiko in [1]. SH supports
> >    neither CONFIG_KEXEC_FILE nor CONFIG_CRASH_HOTPLUG, so skip marking when
> >    both are disabled.
> > 
> > v6 --> v8 (v7 mainly tried to fix the initrd issue on release in v6,
> > that approach is superseded here):
> > 1. Stop marking /memreserve/ regions with NODUMP. v6 marked
> >    /memreserve/ regions with NODUMP. But a bootloader may specify
> >    a /memreserve/ entry for memory that the kernel later frees
> >    (e.g. the initrd), and those pages would then be wrongly
> >    filtered out of the vmcore after being reused as normal memory.
> >    The v7 fix (clearing the flag in free_reserved_area()) caused
> >    a lockless runtime mutation of memblock.memory [2]. Better solutions
> >    exist but need extra preparation, so temporarily dropped the patch
> >    that introduced the problem to keep this series simple in v8.
> > 2. Fix a build failure in patch 2 with both ARCH_KEEP_MEMBLOCK and
> >    MEMORY_HOTPLUG are unset. There the memblock arrays live in
> >    .init.data, and the weak defaults referencing them create section
> >    mismatches, which turn into build errors when SECTION_MISMATCH_WARN_ONLY
> >    is also unset.
> > 3. RISCV recently gained crash hotplug support, so adapt its handler
> >    like x86 in patch 3: use __crash_prepare_headers() instead of
> >    crash_prepare_headers() to avoid self-deadlock.
> > 4. Update the cover letter per review feedback: describe how ACPI
> >    systems filter reserved memory and why a new flag is needed
> >    instead of reusing NOMAP.
> > 
> > v6 --> v7:
> > 1. Fix a stale MEMBLOCK_NODUMP flag issue [3]. Memory reserved and
> >    marked as NODUMP may later be freed (the initrd, for example),
> >    so the NODUMP flag must be cleared accordingly. Since the fix is
> >    part of the NODUMP infrastructure introduced by patch 5, it has
> >    been folded into that patch.
> > 2. Drop the "generic" related description in the cover letter.
> > 3. Collect the Acked-by and Reviewed-by tags received during the v6
> >    review (thanks to Baoquan, Mike, Rob and Marek). Patch 5 is the
> >    only one without a tag, as its Reviewed-by was dropped when the
> >    fix was folded in.
> > 4. Drop patch 1 of v6, which has been merged separately.
> > 
> > 
> > v5 --> v6:
> > 1. Serialize crash header preparation against memory hotplug to avoid
> >    out-of-bounds or use-after-free issues.
> > 2. MEMBLOCK_NODUMP marking is now done after memblock allows resizing,
> >    avoiding a panic from too few regions before resize is permitted.
> > 3. Reordered the patches, put pre-existing bugfixes earlier in the series.
> > 
> > [1] https://sashiko.dev/#/patchset/20261016061549.4181390-1-chenwandun1@gmail.com?part=7
> > [2] https://lore.kernel.org/lkml/20260922090252.B01541F000FF@smtp.kernel.org/
> > [3] https://sashiko.dev/#/message/20260917220750.GA4013814-robh%40kernel.org
> > 
> > v5: https://lore.kernel.org/lkml/20260806093519.2907771-1-chenwandun1@gmail.com/
> > v4: https://lore.kernel.org/lkml/20260630074715.4126796-1-chenwandun1@gmail.com/
> > 
> > Wandun Chen (8):
> >   riscv: build crash_mem ranges from memblock instead of resource tree
> >   crash_core: fold duplicated memblock arch hooks into the weak default
> >   crash_core: serialize crash header preparation against hotplug
> >   crash_core: replace for_each_mem_range() with for_each_mem_region()
> >   memblock: introduce MEMBLOCK_NODUMP flag
> >   of: reserved_mem: add dumpable flag to opt-in vmcore
> >   of: reserved_mem: mark /reserved-memory entries with MEMBLOCK_NODUMP
> >   crash_core: skip MEMBLOCK_NODUMP regions when building vmcore ELF
> >     header
> > 
> >  arch/arm64/kernel/machine_kexec_file.c     | 29 ------------
> >  arch/loongarch/kernel/machine_kexec_file.c | 27 -----------
> >  arch/riscv/Kconfig                         |  2 +-
> >  arch/riscv/kernel/crash.c                  |  2 +-
> >  arch/riscv/kernel/machine_kexec_file.c     | 33 --------------
> >  arch/x86/kernel/crash.c                    |  2 +-
> >  drivers/of/fdt.c                           |  1 +
> >  drivers/of/of_private.h                    |  1 +
> >  drivers/of/of_reserved_mem.c               | 18 ++++++++
> >  include/linux/crash_core.h                 |  2 +
> >  include/linux/memblock.h                   |  9 ++++
> >  include/linux/of_reserved_mem.h            |  1 +
> >  kernel/crash_core.c                        | 53 +++++++++++++++++++++-
> >  kernel/dma/contiguous.c                    |  1 +
> >  mm/memblock.c                              | 16 +++++++
> >  15 files changed, 103 insertions(+), 94 deletions(-)
> > 
> 

-- 
Sincerely yours,
Mike.