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| author | Peter Maydell <peter.maydell@linaro.org> | 2020-11-12 14:40:35 +0000 |
|---|---|---|
| committer | Peter Maydell <peter.maydell@linaro.org> | 2020-11-23 11:07:41 +0000 |
| commit | 71266bb4e9468662d88739827c78fcb37285c643 (patch) | |
| tree | c772b7262a786f8a763a1a4c0bc1f7079acb77c9 /docs/virtio-pmem.rst | |
| parent | 392d8e95c7dd3de10a20387914ac34cb12d8ff04 (diff) | |
docs: Move virtio-pmem.rst into the system manual
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Diffstat (limited to 'docs/virtio-pmem.rst')
| -rw-r--r-- | docs/virtio-pmem.rst | 76 |
1 files changed, 0 insertions, 76 deletions
diff --git a/docs/virtio-pmem.rst b/docs/virtio-pmem.rst deleted file mode 100644 index 4bf5d00443..0000000000 --- a/docs/virtio-pmem.rst +++ /dev/null @@ -1,76 +0,0 @@ - -======================== -QEMU 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. - -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. - -o How does virtio-pmem compare to the nvdimm emulation supported by QEMU? - - 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:: - - -object memory-backend-file,id=mem1,share,mem-path=./virtio_pmem.img,size=4G - -device virtio-pmem-pci,memdev=mem1,id=nv1 - - where: - - - "object memory-backend-file,id=mem1,share,mem-path=<image>, size=<image size>" - creates a backend file with the specified size. - - - "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. - -Hotplug -------- - -Virtio pmem devices can be hotplugged via the QEMU monitor. First, the -memory backing has to be added via 'object_add'; afterwards, the virtio -pmem device can be added via 'device_add'. - -For example, the following commands add another 4GB virtio pmem device to -the guest:: - - (qemu) object_add memory-backend-file,id=mem2,share=on,mem-path=virtio_pmem2.img,size=4G - (qemu) device_add virtio-pmem-pci,id=virtio_pmem2,memdev=mem2 - -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. - - 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. -- ndctl command is not supported. |