Re: [PATCH] docs: sysctl: Add documentation for /proc/sys/xen/

[Jürgen Groß <jgross@xxxxxxxx>]

On 04.03.26 15:16, Shubham Chakraborty wrote:
> Add documentation for the Xen hypervisor sysctl controls in
> /proc/sys/xen/balloon/.
>
> Documents the hotplug_unpopulated tunable (available when
> CONFIG_XEN_BALLOON_MEMORY_HOTPLUG is enabled) which controls
> whether unpopulated memory regions are automatically hotplugged
> when the Xen balloon driver needs to reclaim memory.
>
> The documentation is based on source code analysis of
> drivers/xen/balloon.c.
>
> Signed-off-by: Shubham Chakraborty <chakrabortyshubham66@xxxxxxxxx>
> ---
>   Documentation/admin-guide/sysctl/index.rst |  3 +-
>   Documentation/admin-guide/sysctl/xen.rst   | 33 ++++++++++++++++++++++
>   2 files changed, 35 insertions(+), 1 deletion(-)
>   create mode 100644 Documentation/admin-guide/sysctl/xen.rst
>
> diff --git a/Documentation/admin-guide/sysctl/index.rst 
> b/Documentation/admin-guide/sysctl/index.rst
> index 4dd2c9b5d752..aae68373902f 100644
> --- a/Documentation/admin-guide/sysctl/index.rst
> +++ b/Documentation/admin-guide/sysctl/index.rst
> @@ -84,7 +84,7 @@ sunrpc/               SUN Remote Procedure Call (NFS)
>   user/         Per user namespace limits
>   vm/           memory management tuning
>                 buffer and cache management
> -xen/           <undocumented>
> +xen/           Xen hypervisor controls
>   =============== 
> ===============================================================
>   
>   These are the subdirs I have on my system or have been discovered by
> @@ -102,3 +102,4 @@ it :-)
I think you edited the patch file, but this wasn't improving it. :-)

Please resend without additions making it malformed.

>      sunrpc
>      user
>      vm
> +   xen
> diff --git a/Documentation/admin-guide/sysctl/xen.rst 
> b/Documentation/admin-guide/sysctl/xen.rst
> new file mode 100644
> index 000000000000..957febd6bab9
> --- /dev/null
> +++ b/Documentation/admin-guide/sysctl/xen.rst
> @@ -0,0 +1,33 @@
> +===============
> +/proc/sys/xen/
> +===============
> +
> +These files show up in ``/proc/sys/xen/``, depending on the
> +kernel configuration:
> +
> +.. contents:: :local:
> +
> +balloon/hotplug_unpopulated
> +===========================
> +
> +This flag controls whether unpopulated memory ranges are automatically
> +hotplugged as system RAM.
> +
> +- ``0``: Unpopulated ranges are not hotplugged (default).
> +- ``1``: Unpopulated ranges are automatically hotplugged.
> +
> +When enabled, the Xen balloon driver will add memory regions that are
> +marked as unpopulated in the Xen memory map to the system as usable RAM.
> +This allows for dynamic memory expansion in Xen guest domains.
> +
> +This option is only available when the kernel is built with
> +``CONFIG_XEN_BALLOON_MEMORY_HOTPLUG`` enabled.
The stuff below doesn't seem appropriate here, too. I think it can be
either dropped, or should move up in the file.

> +
> +Copyright (c) 2026, Shubham Chakraborty <chakrabortyshubham66@xxxxxxxxx>
> +
> +For general info and legal blurb, please look in
> +Documentation/admin-guide/sysctl/index.rst.
> +
> +.. See scripts/check-sysctl-docs to keep this up to date:
> +.. scripts/check-sysctl-docs -vtable="xen" \
> +..         $(git grep -l register_sysctl_)

Juergen

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