On Mon, 02 Mar 2015 10:59:59 +0100 Paulo Ricardo Paz Vital <paulo.vi...@profitbricks.com> wrote:
> In addition to Eric's review. > > On Thu, 2015-02-26 at 14:49 -0500, Luiz Capitulino wrote: > > This document describes how to use memory hotplug in QEMU. > > > > Signed-off-by: Luiz Capitulino <lcapitul...@redhat.com> > > --- > > docs/memory-hotplug.txt | 77 > > +++++++++++++++++++++++++++++++++++++++++++++++++ > > 1 file changed, 77 insertions(+) > > create mode 100644 docs/memory-hotplug.txt > > > > diff --git a/docs/memory-hotplug.txt b/docs/memory-hotplug.txt > > new file mode 100644 > > index 0000000..e821449 > > --- /dev/null > > +++ b/docs/memory-hotplug.txt > > @@ -0,0 +1,77 @@ > > +QEMU memory hotplug > > Not sure, but I guess the correct term is "hot plug" or "hot-plug". The > same approach should be used to "hot unplug" or "hot-unplug" and in the > first patch. Someone with better knowledge in English grammar than me > certainly can correct this. :-D Linux seems to call it hotplug in most docs. I have the impression that we have used hotplug too in docs, changelog and code. Although we also use hot-plug sometimes. As long as the doc can serve users well, I really don't care. I'll stick to hotplug, and had one inconsistency to fix. I've fixed the other errors you found. > > +=================== > > + > > +This document explains how to use the memory hotplug feature in QEMU, > > +which is present since v2.1.0. > > + > > +Please, note that memory hot unplug is not supported yet. This means > > +that you're able to add memory, but you're not able to remove it. > > +Also, proper proper guest support is required for memory hotplug > > There are two "proper" words here. > > > +to work. > > + > > +Basic RAM hotplug > > +----------------- > > + > > +In order to be able to hotplug memory, QEMU has to be told how many > > +hotpluggable memory slots to create and what is the maximum amount of > > Following the grammar question above, this should be "hot pluggable" or > "hot-pluggable". > > > +memory the guest can grow. This is done at startup time by means of > > +the -m command-line option, which has the following format: > > + > > + -m [size=]megs[,slots=n,maxmem=size] > > + > > +Where, > > + > > + - "megs" is the startup RAM. It is the RAM the guest will boot with > > + - "slots" is the number of hotpluggable memory slots > > + - "maxmem" is the maximum RAM size the guest can grow > > + > > +For example, the following command-line: > > + > > + qemu [...] 1G,slots=3,maxmem=4G > > + > > +Creates a guest with 1GB of memory and three hotpluggable memory slots. > > +The hotpluggable memory slots are empty when the guest is booted, so all > > +memory the guest will see after boot is 1GB. The maximum memory the > > +guest can reach is 4GB. This means that three additional gigas can be > > +hotplugged by using any combination of the available memory slots. > > + > > +Two monitor commands are used to hotplug memory: > > + > > + - "object_add": creates a memory backend object > > + - "device_add": creates the front-end pc-dimm device and inserts it > > + into an empty slot > > s/the front-end/a front-end > > > + > > +For example, the following commands add another 1GB to the guest > > +discussed earlier: > > + > > + (qemu) object_add memory-backend-ram,id=mem1,size=1G > > + (qemu) device_add pc-dimm,id=dimm1,memdev=mem1 > > + > > +Using the file backend > > +---------------------- > > + > > +Besides basic RAM hotplug, QEMU also supports using files as a memory > > +backend. This is useful for using hugetlbfs in Linux, which provides > > +access to bigger page sizes. > > + > > +For example, assuming that the host has 1GB hugepages available in > > +the /mnt/hugepages-1GB directory, a 1GB hugepage could be hotplugged > > +into the guest from the previous section with the following commnands: > > + > > + (qemu) object_add > > memory-backend-file,id=mem1,size=1G,mem-path=/mnt/hugepages-1GB > > + (qemu) device_add pc-dimm,id=dimm1,memdev=mem1 > > + > > +It's also possible to start a guest with memory plugged into the > > +hotpluggable memory slots. This might seem counterintuitive at first, > > +but this allows for a lot of flexibility when using the file backend. > > + > > +In the following command-line example, a 8GB guest is created where 6GB > > +comes from regular RAM, 1GB is a 1GB hugepage page and 256MB is from > > +2MB pages. Also, the guest has additional memory slots to hotplug more > > +2GB if needed: > > + > > + qemu [...] -m 6GB,slots=4,maxmem=10G \ > > + -object memory-backend-file,id=mem1,size=1G,mem-path=/mnt/hugepages-1G \ > > + -device pc-dimm,id=dimm1,memdev=mem1 \ > > + -object > > memory-backend-file,id=mem2,size=256M,mem-path=/mnt/hugepages-2MB \ > > + -device pc-dimm,id=dimm2,memdev=mem2 >
