From: Yulei Zhang <yuleixzhang@xxxxxxxxxxx>
Introduce dmemfs.rst to document the basic usage of dmemfs.
Signed-off-by: Yulei Zhang <yuleixzhang@xxxxxxxxxxx>
---
Documentation/filesystems/dmemfs.rst | 58 ++++++++++++++++++++++++++++++++++++
Documentation/filesystems/index.rst | 1 +
2 files changed, 59 insertions(+)
create mode 100644 Documentation/filesystems/dmemfs.rst
diff --git a/Documentation/filesystems/dmemfs.rst b/Documentation/filesystems/dmemfs.rst
new file mode 100644
index 00000000..f13ed0c
--- /dev/null
+++ b/Documentation/filesystems/dmemfs.rst
@@ -0,0 +1,58 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=====================================
+The Direct Memory Filesystem - DMEMFS
+=====================================
+
+
+.. Table of contents
+
+ - Overview
+ - Compilation
+ - Usage
+
+Overview
+========
+
+Dmemfs (Direct Memory filesystem) is device memory or reserved
+memory based filesystem. This kind of memory is special as it
+is not managed by kernel and it is without 'struct page'. Therefore
+it can save extra memory from the host system for various usage,
+especially for guest virtual machines.
+
+It uses a kernel boot parameter ``dmem=`` to reserve the system
+memory when the host system boots up, the details can be checked
+in /Documentation/admin-guide/kernel-parameters.txt.
+
+Compilation
+===========
+
+The filesystem should be enabled by turning on the kernel configuration
+options::
+
+ CONFIG_DMEM_FS - Direct Memory filesystem support
+ CONFIG_DMEM - Allow reservation of memory for dmem
+
+
+Additionally, the following can be turned on to aid debugging::
+
+ CONFIG_DMEM_DEBUG_FS - Enable debug information for dmem
+
+Usage
+========
+
+Dmemfs supports mapping ``4K``, ``2M`` and ``1G`` size of pages to
+the userspace, for example ::
+
+ # mount -t dmemfs none -o pagesize=4K /mnt/
+
+The it can create the backing storage with 4G size ::
+
+ # truncate /mnt/dmemfs-uuid --size 4G
+
+To use as backing storage for virtual machine starts with qemu, just need
+to specify the memory-backed-file in the qemu command line like this ::
+
+ # -object memory-backend-file,id=ram-node0,mem-path=/mnt/dmemfs-uuid \
+ share=yes,size=4G,host-nodes=0,policy=preferred -numa node,nodeid=0,memdev=ram-node0
+
diff --git a/Documentation/filesystems/index.rst b/Documentation/filesystems/index.rst
index 98f59a8..23e944b 100644
--- a/Documentation/filesystems/index.rst
+++ b/Documentation/filesystems/index.rst
@@ -120,3 +120,4 @@ Documentation for filesystem implementations.
xfs-delayed-logging-design
xfs-self-describing-metadata
zonefs
+ dmemfs
--
1.8.3.1
