From: Breno Leitao <leitao@debian•org>
To: Jinjie Ruan <ruanjinjie@huawei•com>
Cc: corbet@lwn•net, skhan@linuxfoundation•org,
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Subject: Re: [PATCH v9 4/5] arm64: kexec: Add support for crashkernel CMA reservation
Date: Mon, 23 Mar 2026 09:42:38 -0700 [thread overview]
Message-ID: <acFtMLyCWbYOyFZT@gmail.com> (raw)
In-Reply-To: <a5694ee0-7a95-4c15-6775-990d70c8d77b@huawei.com>
On Mon, Mar 23, 2026 at 07:17:21PM +0800, Jinjie Ruan wrote:
>
>
> On 2026/3/23 18:20, Breno Leitao wrote:
> > On Mon, Mar 23, 2026 at 03:27:44PM +0800, Jinjie Ruan wrote:
> >> Commit 35c18f2933c5 ("Add a new optional ",cma" suffix to the
> >> crashkernel= command line option") and commit ab475510e042 ("kdump:
> >> implement reserve_crashkernel_cma") added CMA support for kdump
> >> crashkernel reservation.
> >>
> >> Crash kernel memory reservation wastes production resources if too
> >> large, risks kdump failure if too small, and faces allocation difficulties
> >> on fragmented systems due to contiguous block constraints. The new
> >> CMA-based crashkernel reservation scheme splits the "large fixed
> >> reservation" into a "small fixed region + large CMA dynamic region": the
> >> CMA memory is available to userspace during normal operation to avoid
> >> waste, and is reclaimed for kdump upon crash—saving memory while
> >> improving reliability.
> >>
> >> So extend crashkernel CMA reservation support to arm64. The following
> >> changes are made to enable CMA reservation:
> >>
> >> - Parse and obtain the CMA reservation size along with other crashkernel
> >> parameters.
> >> - Call reserve_crashkernel_cma() to allocate the CMA region for kdump.
> >> - Include the CMA-reserved ranges for kdump kernel to use.
> >> - Exclude the CMA-reserved ranges from the crash kernel memory to
> >> prevent them from being exported through /proc/vmcore, which is already
> >> done in the crash core.
> >>
> >> Update kernel-parameters.txt to document CMA support for crashkernel on
> >> arm64 architecture.
> >>
> >> Acked-by: Rob Herring (Arm) <robh@kernel•org>
> >> Acked-by: Baoquan He <bhe@redhat•com>
> >> Acked-by: Mike Rapoport (Microsoft) <rppt@kernel•org>
> >> Acked-by: Ard Biesheuvel <ardb@kernel•org>
> >> Signed-off-by: Jinjie Ruan <ruanjinjie@huawei•com>
> >> ---
> >> v7:
> >> - Correct the inclusion of CMA-reserved ranges for kdump
> >> kernel in of/kexec.
> >> v3:
> >> - Add Acked-by.
> >> v2:
> >> - Free cmem in prepare_elf_headers()
> >> - Add the mtivation.
> >> ---
> >> Documentation/admin-guide/kernel-parameters.txt | 2 +-
> >> arch/arm64/kernel/machine_kexec_file.c | 2 +-
> >> arch/arm64/mm/init.c | 5 +++--
> >> drivers/of/fdt.c | 9 +++++----
> >> drivers/of/kexec.c | 9 +++++++++
> >> 5 files changed, 19 insertions(+), 8 deletions(-)
> >>
> >> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> >> index cb850e5290c2..afb3112510f7 100644
> >> --- a/Documentation/admin-guide/kernel-parameters.txt
> >> +++ b/Documentation/admin-guide/kernel-parameters.txt
> >> @@ -1121,7 +1121,7 @@ Kernel parameters
> >> It will be ignored when crashkernel=X,high is not used
> >> or memory reserved is below 4G.
> >> crashkernel=size[KMG],cma
> >> - [KNL, X86, ppc] Reserve additional crash kernel memory from
> >> + [KNL, X86, ARM64, PPC] Reserve additional crash kernel memory from
> >> CMA. This reservation is usable by the first system's
> >> userspace memory and kernel movable allocations (memory
> >> balloon, zswap). Pages allocated from this memory range
> >> diff --git a/arch/arm64/kernel/machine_kexec_file.c b/arch/arm64/kernel/machine_kexec_file.c
> >> index c338506a580b..cc577d77df00 100644
> >> --- a/arch/arm64/kernel/machine_kexec_file.c
> >> +++ b/arch/arm64/kernel/machine_kexec_file.c
> >> @@ -42,7 +42,7 @@ int arch_kimage_file_post_load_cleanup(struct kimage *image)
> >> #ifdef CONFIG_CRASH_DUMP
> >> unsigned int arch_get_system_nr_ranges(void)
> >> {
> >> - unsigned int nr_ranges = 2; /* for exclusion of crashkernel region */
> >> + unsigned int nr_ranges = 2 + crashk_cma_cnt; /* for exclusion of crashkernel region */
> >
> > You update arch_get_system_nr_ranges() to account for CMA ranges, but
> > prepare_elf_headers() in the same file (line 51) still has the
> > hardcoded:
> >
> > nr_ranges = 2; /* for exclusion of crashkernel region */
>
> I don't see any logic related to prepare_elf_headers() or hardcoded
> nr_ranges = 2 in the arm64 implementation.
Just ignore me here, I've mis applied the patch, and then I got
arch_get_system_nr_ranges() and prepare_elf_headers(), but, they are the
same thing at in here.
> >
> > and does not exclude CMA ranges from cmem. If the generic crash core
> > handles CMA exclusion from vmcore, then shouldn't
> > arch_get_system_nr_ranges() also not need this change?
> >
next prev parent reply other threads:[~2026-03-23 16:44 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-03-23 7:27 [PATCH v9 0/5] arm64/riscv: Add support for crashkernel CMA reservation Jinjie Ruan
2026-03-23 7:27 ` [PATCH v9 1/5] powerpc/crash: sort crash memory ranges before preparing elfcorehdr Jinjie Ruan
2026-03-23 7:27 ` [PATCH v9 2/5] crash: Exclude crash kernel memory in crash core Jinjie Ruan
2026-03-23 7:27 ` [PATCH v9 3/5] crash: Use crash_exclude_core_ranges() on powerpc Jinjie Ruan
2026-03-23 7:27 ` [PATCH v9 4/5] arm64: kexec: Add support for crashkernel CMA reservation Jinjie Ruan
2026-03-23 10:20 ` Breno Leitao
2026-03-23 11:17 ` Jinjie Ruan
2026-03-23 16:42 ` Breno Leitao [this message]
2026-03-23 7:27 ` [PATCH v9 5/5] riscv: " Jinjie Ruan
2026-03-23 16:55 ` [PATCH v9 0/5] arm64/riscv: " Andrew Morton
2026-03-24 4:02 ` Jinjie Ruan
2026-03-24 4:29 ` Sourabh Jain
2026-03-24 6:14 ` Jinjie Ruan
2026-03-24 6:35 ` Askar Safin
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