[35/35] Add documentation for dmemfs

Commit Message

yulei zhang Oct. 8, 2020, 7:54 a.m. UTC

From: Yulei Zhang <[e-mail]>

Introduce dmemfs.rst to document the basic usage of dmemfs.

Signed-off-by: Yulei Zhang <[e-mail]>
---
 Documentation/filesystems/dmemfs.rst | 59 ++++++++++++++++++++++++++++
 1 file changed, 59 insertions(+)
 create mode 100644 Documentation/filesystems/dmemfs.rst

Comments

Randy Dunlap Oct. 9, 2020, 1:26 a.m. UTC | #1

On 10/8/20 12:54 AM, [e-mail] wrote:
> From: Yulei Zhang <[e-mail]>
> 
> Introduce dmemfs.rst to document the basic usage of dmemfs.
> 

Please add dmemfs as an entry in Documentation/filesystems/index.rst also.

> Signed-off-by: Yulei Zhang <[e-mail]>
> ---
>  Documentation/filesystems/dmemfs.rst | 59 ++++++++++++++++++++++++++++
>  1 file 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 000000000000..cbb4cc1ed31d
> --- /dev/null
> +++ b/Documentation/filesystems/dmemfs.rst
> @@ -0,0 +1,57 @@
> +.. 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,

                                                             usages,

> +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

                                     up. The details

> +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

Hm, is there a good reason for having both of these options?
Is one of them usable without the other one?
If not, there should only be one Kconfig option for DMEMFS.

> +
> +
> +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 ::

   Then

> +
> +    # 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
>

Patch

diff --git a/Documentation/filesystems/dmemfs.rst b/Documentation/filesystems/dmemfs.rst
new file mode 100644
index 000000000000..cbb4cc1ed31d
--- /dev/null
+++ b/Documentation/filesystems/dmemfs.rst
@@ -0,0 +1,57 @@ 
+.. 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