Re: [PATCH v4 02/10] crash hp: Introduce CRASH_HOTPLUG configuration options

Baoquan He
2022-02-23T03:25:34Z

On 02/09/22 at 02:56pm, Eric DeVolder wrote:
> Support for CPU and memory hotplug for crash is controlled by the
> CRASH_HOTPLUG configuration option, introduced by this patch.
>
> The CRASH_HOTPLUG_ELFCOREHDR_SZ related configuration option is
> also introduced with this patch.
>
> Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
> ---
> arch/x86/Kconfig | 26 ++++++++++++++++++++++++++
> 1 file changed, 26 insertions(+)
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index ebe8fc76949a..4e3374edab02 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -2060,6 +2060,32 @@ config CRASH_DUMP
> (CONFIG_RELOCATABLE=y).
> For more details see Documentation/admin-guide/kdump/kdump.rst
>
> +config CRASH_HOTPLUG
> + bool "kernel updates of crash elfcorehdr"
> + depends on CRASH_DUMP && (HOTPLUG_CPU || MEMORY_HOTPLUG) && KEXEC_FILE
> + help
> + Enable the kernel to update the crash elfcorehdr (which contains
> + the list of CPUs and memory regions) directly when hot plug/unplug
> + of CPUs or memory. Otherwise userspace must monitor these hot
> + plug/unplug change notifications via udev in order to
> + unload-then-reload the crash kernel so that the list of CPUs and
> + memory regions is kept up-to-date. Note that the udev CPU and
> + memory change notifications still occur (however, userspace is not
> + required to monitor for crash dump purposes).
> +
> +config CRASH_HOTPLUG_ELFCOREHDR_SZ
> + depends on CRASH_HOTPLUG
> + int
> + default 131072
> + help
> + Specify the maximum size of the elfcorehdr buffer/segment.
> + The 128KiB default is sized so that it can accommodate 2048
> + Elf64_Phdr, where each Phdr represents either a CPU or a
> + region of memory.
> + For example, this size can accommodate hotplugging a machine
> + with up to 1024 CPUs and up to 1024 memory regions (e.g. 1TiB
> + with 1024 1GiB memory DIMMs).

This example of memory could be a little misleading. The memory regions
may not be related to memory DIMMs. System could split them into many
smaller regions during bootup.

Otherwise, this patch looks good to me.

> +
> config KEXEC_JUMP
> bool "kexec jump"
> depends on KEXEC && HIBERNATION
> --
> 2.27.0
>