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Wed, 04 Mar 2026 06:17:15 -0800 (PST) Received: from localhost.localdomain ([2409:40e5:116b:88d4:1c32:f854:c933:d139]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2ae3d1b2c51sm128138145ad.19.2026.03.04.06.17.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 04 Mar 2026 06:17:12 -0800 (PST) From: Shubham Chakraborty To: corbet@lwn.net, jgross@suse.com Cc: sstabellini@kernel.org, boris.ostrovsky@oracle.com, linux-doc@vger.kernel.org, xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org, Shubham Chakraborty Subject: [PATCH] docs: sysctl: Add documentation for /proc/sys/xen/ Date: Wed, 4 Mar 2026 19:46:44 +0530 Message-Id: <20260304141644.28777-1-chakrabortyshubham66@gmail.com> X-Mailer: git-send-email 2.39.5 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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 --- 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/adm= in-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/ +xen/ Xen hypervisor controls =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D =3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D =20 These are the subdirs I have on my system or have been discovered by @@ -102,3 +102,4 @@ it :-) 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 @@ +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D +/proc/sys/xen/ +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D + +These files show up in ``/proc/sys/xen/``, depending on the +kernel configuration: + +.. contents:: :local: + +balloon/hotplug_unpopulated +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D + +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. + +Copyright (c) 2026, Shubham Chakraborty + +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=3D"xen" \ +.. $(git grep -l register_sysctl_) --=20 2.39.5