linux-kernel - Re: [PATCH v25 06/10] crash: memory and CPU hotplug sysfs attributes

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Message-ID: <c9d4e623-5c8c-885f-4343-980798647a0a@infradead.org>
Date:   Thu, 29 Jun 2023 13:59:05 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Eric DeVolder <eric.devolder@...cle.com>,
        linux-kernel@...r.kernel.org, david@...hat.com, osalvador@...e.de,
        corbet@....net, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, bhe@...hat.com,
        ebiederm@...ssion.com, kexec@...ts.infradead.org
Cc:     hpa@...or.com, gregkh@...uxfoundation.org, rafael@...nel.org,
        vgoyal@...hat.com, dyoung@...hat.com, lf32.dev@...il.com,
        akpm@...ux-foundation.org, naveen.n.rao@...ux.vnet.ibm.com,
        zohar@...ux.ibm.com, bhelgaas@...gle.com, vbabka@...e.cz,
        tiwai@...e.de, seanjc@...gle.com, linux@...ssschuh.net,
        vschneid@...hat.com, linux-mm@...ck.org, linux-doc@...r.kernel.org,
        sourabhjain@...ux.ibm.com, konrad.wilk@...cle.com,
        boris.ostrovsky@...cle.com
Subject: Re: [PATCH v25 06/10] crash: memory and CPU hotplug sysfs attributes

Hi--

On 6/29/23 12:21, Eric DeVolder wrote:
> 
> Signed-off-by: Eric DeVolder <eric.devolder@...cle.com>
> Reviewed-by: Sourabh Jain <sourabhjain@...ux.ibm.com>
> Acked-by: Hari Bathini <hbathini@...ux.ibm.com>
> Acked-by: Baoquan He <bhe@...hat.com>
> ---
>  Documentation/ABI/testing/sysfs-devices-memory |  8 ++++++++
>  .../ABI/testing/sysfs-devices-system-cpu       |  8 ++++++++
>  .../admin-guide/mm/memory-hotplug.rst          |  8 ++++++++
>  Documentation/core-api/cpu_hotplug.rst         | 18 ++++++++++++++++++
>  drivers/base/cpu.c                             | 16 ++++++++++++++--
>  drivers/base/memory.c                          | 13 +++++++++++++
>  include/linux/kexec.h                          |  8 ++++++++
>  7 files changed, 77 insertions(+), 2 deletions(-)
> 

> diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst
> index 1b02fe5807cc..eb99d79223a3 100644
> --- a/Documentation/admin-guide/mm/memory-hotplug.rst
> +++ b/Documentation/admin-guide/mm/memory-hotplug.rst
> @@ -291,6 +291,14 @@ The following files are currently defined:
>  		       Availability depends on the CONFIG_ARCH_MEMORY_PROBE
>  		       kernel configuration option.
>  ``uevent``	       read-write: generic udev file for device subsystems.
> +``crash_hotplug``      read-only: when changes to the system memory map
> +		       occur due to hot un/plug of memory, this file contains
> +		       '1' if the kernel updates the kdump capture kernel memory
> +		       map itself (via elfcorehdr), or '0' if userspace must update
> +		       the kdump capture kernel memory map.
> +
> +		       Availability depends on the CONFIG_MEMORY_HOTPLUG kernel
> +		       configuration option.
>  ====================== =========================================================

Did you test build the documentation?
It looks to me like the end-of-table '=' signs line needs 3 more === to be long
enough for the text above it.

>  
>  .. note::
> diff --git a/Documentation/core-api/cpu_hotplug.rst b/Documentation/core-api/cpu_hotplug.rst
> index e6f5bc39cf5c..54581c501562 100644
> --- a/Documentation/core-api/cpu_hotplug.rst
> +++ b/Documentation/core-api/cpu_hotplug.rst
> @@ -741,6 +741,24 @@ will receive all events. A script like::
>  
>  can process the event further.
>  
> +When changes to the CPUs in the system occur, the sysfs file
> +/sys/devices/system/cpu/crash_hotplug contains '1' if the kernel
> +updates the kdump capture kernel list of CPUs itself (via elfcorehdr),
> +or '0' if userspace must update the kdump capture kernel list of CPUs.
> +
> +The availability depends on the CONFIG_HOTPLUG_CPU kernel configuration
> +option.
> +
> +To skip userspace processing of CPU hot un/plug events for kdump
> +(ie the unload-then-reload to obtain a current list of CPUs), this sysfs

    i.e.

> +file can be used in a udev rule as follows:
> +
> + SUBSYSTEM=="cpu", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end"
> +
> +For a cpu hot un/plug event, if the architecture supports kernel updates

         CPU
for consistency

> +of the elfcorehdr (which contains the list of CPUs), then the rule skips
> +the unload-then-reload of the kdump capture kernel.
> +
>  Kernel Inline Documentations Reference
>  ======================================
>  

Thanks.
-- 
~Randy