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authorPeter Maydell <peter.maydell@linaro.org>2020-11-12 14:40:36 +0000
committerPeter Maydell <peter.maydell@linaro.org>2020-11-23 11:07:41 +0000
commitc5d7cfdaace7f547fd572b50baaa7182366513e7 (patch)
tree490446750d9ec5e2ebf4623b2ef8634733706c6f /docs
parent71266bb4e9468662d88739827c78fcb37285c643 (diff)
docs/system/virtio-pmem.rst: Fix minor style issues
The virtio-pmem documentation has some minor style issues we hadn't noticed since we weren't rendering it in our docs: * Sphinx doesn't complain about overlong title-underlining the way it complains about too-short underlining, but it looks odd; make the underlines of section headers the right length * Indent of paragraphs makes them render as blockquotes; remove the indent so they just render as normal text * Leading 'o' isn't rst markup, so it just renders as a literal "o"; reformat as a subsection heading instead * "QEMU" in the document title and section headings are a bit odd and unnecessary since this is the QEMU manual; delete or rephrase them * There's no need to specify what QEMU version the device first appeared in. Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Reviewed-by: Alex Bennée <alex.bennee@linaro.org> Reviewed-by: Pankaj Gupta <pankaj.gupta@cloud.ionos.com>
Diffstat (limited to 'docs')
-rw-r--r--docs/system/virtio-pmem.rst60
1 files changed, 30 insertions, 30 deletions
diff --git a/docs/system/virtio-pmem.rst b/docs/system/virtio-pmem.rst
index 4bf5d00443..c82ac06731 100644
--- a/docs/system/virtio-pmem.rst
+++ b/docs/system/virtio-pmem.rst
@@ -1,38 +1,37 @@
-========================
-QEMU virtio pmem
-========================
+===========
+virtio pmem
+===========
- This document explains the setup and usage of the virtio pmem device
- which is available since QEMU v4.1.0.
-
- The virtio pmem device is a paravirtualized persistent memory device
- on regular (i.e non-NVDIMM) storage.
+This document explains the setup and usage of the virtio pmem device.
+The virtio pmem device is a paravirtualized persistent memory device
+on regular (i.e non-NVDIMM) storage.
Usecase
---------
+-------
- Virtio pmem allows to bypass the guest page cache and directly use
- host page cache. This reduces guest memory footprint as the host can
- make efficient memory reclaim decisions under memory pressure.
+Virtio pmem allows to bypass the guest page cache and directly use
+host page cache. This reduces guest memory footprint as the host can
+make efficient memory reclaim decisions under memory pressure.
-o How does virtio-pmem compare to the nvdimm emulation supported by QEMU?
+How does virtio-pmem compare to the nvdimm emulation?
+-----------------------------------------------------
- NVDIMM emulation on regular (i.e. non-NVDIMM) host storage does not
- persist the guest writes as there are no defined semantics in the device
- specification. The virtio pmem device provides guest write persistence
- on non-NVDIMM host storage.
+NVDIMM emulation on regular (i.e. non-NVDIMM) host storage does not
+persist the guest writes as there are no defined semantics in the device
+specification. The virtio pmem device provides guest write persistence
+on non-NVDIMM host storage.
virtio pmem usage
-----------------
- A virtio pmem device backed by a memory-backend-file can be created on
- the QEMU command line as in the following example::
+A virtio pmem device backed by a memory-backend-file can be created on
+the QEMU command line as in the following example::
-object memory-backend-file,id=mem1,share,mem-path=./virtio_pmem.img,size=4G
-device virtio-pmem-pci,memdev=mem1,id=nv1
- where:
+where:
- "object memory-backend-file,id=mem1,share,mem-path=<image>, size=<image size>"
creates a backend file with the specified size.
@@ -40,8 +39,8 @@ virtio pmem usage
- "device virtio-pmem-pci,id=nvdimm1,memdev=mem1" creates a virtio pmem
pci device whose storage is provided by above memory backend device.
- Multiple virtio pmem devices can be created if multiple pairs of "-object"
- and "-device" are provided.
+Multiple virtio pmem devices can be created if multiple pairs of "-object"
+and "-device" are provided.
Hotplug
-------
@@ -59,17 +58,18 @@ the guest::
Guest Data Persistence
----------------------
- Guest data persistence on non-NVDIMM requires guest userspace applications
- to perform fsync/msync. This is different from a real nvdimm backend where
- no additional fsync/msync is required. This is to persist guest writes in
- host backing file which otherwise remains in host page cache and there is
- risk of losing the data in case of power failure.
+Guest data persistence on non-NVDIMM requires guest userspace applications
+to perform fsync/msync. This is different from a real nvdimm backend where
+no additional fsync/msync is required. This is to persist guest writes in
+host backing file which otherwise remains in host page cache and there is
+risk of losing the data in case of power failure.
- With virtio pmem device, MAP_SYNC mmap flag is not supported. This provides
- a hint to application to perform fsync for write persistence.
+With virtio pmem device, MAP_SYNC mmap flag is not supported. This provides
+a hint to application to perform fsync for write persistence.
Limitations
-------------
+-----------
+
- Real nvdimm device backend is not supported.
- virtio pmem hotunplug is not supported.
- ACPI NVDIMM features like regions/namespaces are not supported.