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Reflect in virtiofs.rst that virtiofs can be used without NUMA

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Reflect in the virtiofs documentation that virtiofs can now be used
even without NUMA. While at it, be more precise where and why shared
memory is required.

Signed-off-by: Halil Pasic <pasic@linux.ibm.com>
Signed-off-by: Marc Hartmayer <mhartmay@linux.ibm.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
This commit is contained in:
Halil Pasic 2020-10-13 18:53:12 +02:00 committed by Michal Privoznik
parent e2425a1727
commit 5d787acbf0
1 changed files with 12 additions and 5 deletions
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17
docs/kbase/virtiofs.rst
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@ -16,10 +16,17 @@ See https://virtio-fs.gitlab.io/
Host setup
==========
The host-side virtiofsd daemon, like other vhost-user backed devices,
requires shared memory between the host and the guest. As of QEMU 4.2, this
requires specifying a NUMA topology for the guest and explicitly specifying
a memory backend. Multiple options are available:
Almost all virtio devices (all that use virtqueues) require access to
at least certain portions of guest RAM (possibly policed by DMA). In
case of virtiofsd, much like in case of other vhost-user (see
https://www.qemu.org/docs/master/interop/vhost-user.html) virtio
devices that are realized by an userspace process, this in practice
means that QEMU needs to allocate the backing memory for all the guest
RAM as shared memory. As of QEMU 4.2, it is possible to explicitly
specify a memory backend when specifying the NUMA topology. This
method is however only viable for machine types that do support
NUMA. As of QEMU 5.0.0, it is possible to specify the memory backend
without NUMA (using the so called memobject interface).
Either of the following:
@ -46,7 +53,7 @@ Either of the following:
Guest setup
===========
#. Specify the NUMA topology
#. Specify the NUMA topology (this step is only required for the NUMA case)
in the domain XML of the guest.
For the simplest one-node topology for a guest with 2GiB of RAM and 8 vCPUs: