From c5d7cfdaace7f547fd572b50baaa7182366513e7 Mon Sep 17 00:00:00 2001 From: Peter Maydell Date: Thu, 12 Nov 2020 14:40:36 +0000 Subject: [PATCH] docs/system/virtio-pmem.rst: Fix minor style issues MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Reviewed-by: Alex Bennée Reviewed-by: Pankaj Gupta --- docs/system/virtio-pmem.rst | 60 ++++++++++++++++++------------------- 1 file 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=, 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.