2:58 a.m.
I am trying to create a VM with added persistent memory using virsh. It
fails when persistent memory namespace size is larger than available system
memory. Please see error below, prealloc=yes is set in the command line.
For dax type namespace, as I understand, prealloc should not be needed. Is
this support to add persistent memory implemented in virsh? If so, how to
set prealloc=no? Anything else needed to add in xml for persistent memory?
Thanks.
1. dax namespace (400GB) which is larger than system memory.
# ndctl create-namespace -t pmem -m devdax --align=4k -s 400G {
"dev":"namespace1.0",
"mode":"devdax",
"map":"dev",
"size":"393.75 GiB (422.78 GB)",
"uuid":"00670b70-7871-4749-a901-9184b7a388d8",
"raw_uuid":"a5a1d3f8-01e4-45a2-bad1-38fd09bf4672",
"daxregion":{
"id":1,
"size":"393.75 GiB (422.78 GB)",
"align":4096,
"devices":[
{
"chardev":"dax1.0",
"size":"393.75 GiB (422.78 GB)"
}
]
},
"numa_node":1
}
2. Relevant parts of xml
<domain type='kvm'>
<name>test</name>
<uuid>02c49a19-ce9e-4320-9a6b-1ebf0913a10e</uuid>
<maxMemory slots='16' unit='KiB'>459800576</maxMemory>
<memory unit='KiB'>65536000</memory>
<currentMemory unit='KiB'>65536000</currentMemory>
<vcpu placement='static'>4</vcpu>
<os>
:
:
<cpu mode='custom' match='exact' check='partial'>
<feature policy='require' name='hypervisor'/>
<numa>
<cell id='0' cpus='0-3' memory='65536000'
unit='KiB'/>
</numa>
</cpu>
:
:
<memory model='nvdimm'>
<source>
<path>/dev/dax1.0</path>
</source>
<target>
<size unit='GiB'>376</size>
<node>0</node>
<label>
<size unit='KiB'>128</size>
</label>
</target>
<address type='dimm' slot='0'/>
</memory>
3. Error:
# virsh start test
error: Failed to start domain test
error: internal error: qemu unexpectedly closed the monitor: ftruncate:
Invalid argument 2019-08-22T04:16:08.744402Z qemu-system-x86_64: -object
memory-backend-file,id=memnvdimm0,prealloc=yes,mem-path=/dev/dax1.0,size=403726925824:
unable to map backing store for guest RAM: Cannot allocate memory
Virsh version 4.7.0, qemu version 3.0.0
8:19 a.m.
On 8/27/19 9:58 AM, Seema Pandit wrote:
error: internal error: qemu unexpectedly closed the monitor:
ftruncate:
Invalid argument 2019-08-22T04:16:08.744402Z qemu-system-x86_64: -object
memory-backend-file,id=memnvdimm0,prealloc=yes,mem-path=/dev/dax1.0,size=403726925824:
unable to map backing store for guest RAM: Cannot allocate memory
I wonder if dropping 'prealloc' would help. This error message comes
from phase before 'prealloc' is processed. You can try the following
patch:
diff --git i/src/qemu/qemu_command.c w/src/qemu/qemu_command.c
index 373ebd6d1a..c375955eab 100644
--- i/src/qemu/qemu_command.c
+++ w/src/qemu/qemu_command.c
@@ -3468,7 +3468,7 @@ qemuBuildMemoryBackendProps(virJSONValuePtr *backendProps,
}
if (virJSONValueObjectAdd(props,
- "B:prealloc", prealloc,
+ "B:prealloc", prealloc ? false : false,
"s:mem-path", memPath,
NULL) < 0)
goto cleanup;
Michal
12:33 p.m.
Hi Michal,
Thank you for the reply.
I was having issues compiling qemu code on fedora29. So instead of dropping
prealloc in virsh, tried adding prealloc=yes in qemu command line.
prealloc=yes works. It does not lead to using more system memory when using
DAX.
+Dan
Here are the steps:
ndctl create-namespace -t pmem -m fsdax --align=4k -s 400G
mkfs.ext4 /dev/pmem0
mount -o dax /dev/pmem0 /mnt/pmem0
dd if=/dev/zero of=/mnt/pmem0/file1 bs=4k count=104857600
[root@system-name]# dd if=/dev/zero of=/mnt/pmem0/file1 bs=4k
count=104857600
dd: error writing '/mnt/pmem0/file1': No space left on device
101313980+0 records in
101313979+0 records out
414982057984 bytes (415 GB, 386 GiB) copied, 946.495 s, 438 MB/s
Slightly smaller file is created than asked.
[root@system-name]# du -sh
387G .
sample qemu command line which works:
qemu-system-x86_64 \
-name test \
-drive
file=/var/lib/libvirt/images/test-ad.qcow2,format=qcow2,index=0,media=disk
\ -m 2G,slots=4,maxmem=428G \ -smp 2 \ -machine pc,accel=kvm,nvdimm=on \
-enable-kvm \ -object
memory-backend-file,id=pmem1,prealloc=yes,share=on,mem-path=/mnt/pmem0/file1,size=386G,align=4K
\ -device nvdimm,memdev=pmem1,id=nv1 \ -daemonize
So prealloc option works.
But still passing /mnt/pmem0/file1 in virsh as the nvdimm fails to start
the VM. Errors out saying cannot allocate that much memory.
On Wed, Aug 28, 2019 at 6:49 PM Michal Privoznik <mprivozn(a)redhat.com>
wrote:
On 8/27/19 9:58 AM, Seema Pandit wrote:
> error: internal error: qemu unexpectedly closed the monitor: ftruncate:
> Invalid argument 2019-08-22T04:16:08.744402Z qemu-system-x86_64: -object
>
memory-backend-file,id=memnvdimm0,prealloc=yes,mem-path=/dev/dax1.0,size=403726925824:
> unable to map backing store for guest RAM: Cannot allocate memory
I wonder if dropping 'prealloc' would help. This error message comes
from phase before 'prealloc' is processed. You can try the following
patch:
diff --git i/src/qemu/qemu_command.c w/src/qemu/qemu_command.c
index 373ebd6d1a..c375955eab 100644
--- i/src/qemu/qemu_command.c
+++ w/src/qemu/qemu_command.c
@@ -3468,7 +3468,7 @@ qemuBuildMemoryBackendProps(virJSONValuePtr
*backendProps,
}
if (virJSONValueObjectAdd(props,
- "B:prealloc", prealloc,
+ "B:prealloc", prealloc ? false : false,
"s:mem-path", memPath,
NULL) < 0)
goto cleanup;
Michal
1:51 a.m.
On 8/31/19 7:33 PM, Seema Pandit wrote:
Hi Michal,
Thank you for the reply.
I was having issues compiling qemu code on fedora29. So instead of dropping
prealloc in virsh, tried adding prealloc=yes in qemu command line.
prealloc=yes works. It does not lead to using more system memory when using
DAX.
+Dan
Here are the steps:
ndctl create-namespace -t pmem -m fsdax --align=4k -s 400G
mkfs.ext4 /dev/pmem0
mount -o dax /dev/pmem0 /mnt/pmem0
dd if=/dev/zero of=/mnt/pmem0/file1 bs=4k count=104857600
[root@system-name]# dd if=/dev/zero of=/mnt/pmem0/file1 bs=4k
count=104857600
dd: error writing '/mnt/pmem0/file1': No space left on device
101313980+0 records in
101313979+0 records out
414982057984 bytes (415 GB, 386 GiB) copied, 946.495 s, 438 MB/s
Slightly smaller file is created than asked.
[root@system-name]# du -sh
387G .
sample qemu command line which works:
qemu-system-x86_64 \
-name test \
-drive
file=/var/lib/libvirt/images/test-ad.qcow2,format=qcow2,index=0,media=disk
\ -m 2G,slots=4,maxmem=428G \ -smp 2 \ -machine pc,accel=kvm,nvdimm=on \
-enable-kvm \ -object
memory-backend-file,id=pmem1,prealloc=yes,share=on,mem-path=/mnt/pmem0/file1,size=386G,align=4K
\ -device nvdimm,memdev=pmem1,id=nv1 \ -daemonize
Looks like the only difference to the cmd line generated by libvirt and
this one then is align=4K. To confirm that, can you share the full qemu
cmd line as generated by libvirt please?
Libvirt does not do anything special with guest memory, so this is
matter of qemu cmd line and that's why we need to see what's different,
what works and what doesn't. Then we have some lead to understand the
problem IMO.
Michal
12:10 p.m.
After adding the memoryBacking tag in xml as below (in addition, to other
xml changes to add nvdimm), virsh could allocate AD memory larger than the
system RAM and VMs could start successfully.
<memoryBacking>
<access mode='shared'/>
<discard/>
</memoryBacking>
This adds share=yes in command line.
-object
memory-backend-file,id=memnvdimm0,prealloc=yes,mem-path=/mnt/pmem0/file1,share=yes,size=414464344064
-device nvdimm,node=0,label-size=131072,memdev=memnvdimm0,id=nvdimm0,slot=0
For reference qemu command line where VM starts quickly:
qemu-system-x86_64 \
-name qemu-gold29 \
-drive
file=/var/lib/libvirt/images/gold29-ad.qcow2,format=qcow2,index=0,media=disk
\ -m 2G,slots=4,maxmem=428G \ -smp 2 \ -machine pc,accel=kvm,nvdimm=on \
-enable-kvm \ -object
memory-backend-file,id=pmem1,share=on,mem-path=/mnt/pmem0/file1,size=386G,align=4K
\ -device nvdimm,memdev=pmem1,id=nv1 \ -daemonize
Qemu command line generated from virsh: (please note VM now starts with
this command line, shared=yes.)
/usr/bin/qemu-system-x86_64 -machine accel=kvm -name
guest=mix-test,debug-threads=on -S -object
secret,id=masterKey0,format=raw,file=/var/lib/libvirt/qemu/domain-18-mix-test/master-key.aes
-machine
pc-i440fx-3.0,accel=kvm,usb=off,vmport=off,dump-guest-core=off,nvdimm=on
-cpu Skylake-Server-IBRS,hypervisor=on -m
size=2097152k,slots=16,maxmem=419430400k -realtime mlock=off -smp
2,sockets=2,cores=1,threads=1 -object
memory-backend-file,id=ram-node0,mem-path=/var/lib/libvirt/qem
/ram/libvirt/qemu/18-mix-test/ram-node0,discard-data=yes,share=yes,size=2147483648
-numa node,nodeid=0,cpus=0-1,memdev=ram-node0 -object
memory-backend-file,id=memnvdimm0,prealloc=yes,mem-path=/mnt/pmem0/file1,share=yes,size=414464344064
-device nvdimm,node=0,label-size=131072,memdev=memnvdimm0,id=nvdimm0,slot=0
-uuid 318c0529-0330-460b-8d0a-3b253e9decdd -no-user-config -nodefaults
-chardev socket,id=charmonitor,fd=32,server,nowait -mon
chardev=charmonitor,id=monitor,mode=control -rtc base=utc,driftfix=slew
-global kvm-pit.lost_tick_policy=delay -no-hpet -no-shutdown -global
PIIX4_PM.disable_s3=1 -global PIIX4_PM.disable_s4=1 -boot strict=on -device
ich9-usb-ehci1,id=usb,bus=pci.0,addr=0x5.0x7 -device
ich9-usb-uhci1,masterbus=usb.0,firstport=0,bus=pci.0,multifunction=on,addr=0x5
-device ich9-usb-uhci2,masterbus=usb.0,firstport=2,bus=pci.0,addr=0x5.0x1
-device ich9-usb-uhci3,masterbus=usb.0,firstport=4,bus=pci.0,addr=0x5.0x2
-device virtio-serial-pci,id=virtio-serial0,bus=pci.0,addr=0x6 -drive
file=/var/lib/libvirt/images/mix-test.qcow2,format=qcow2,if=none,id=drive-virtio-disk0
-device
virtio-blk-pci,scsi=off,bus=pci.0,addr=0x7,drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1
-drive if=none,id=drive-ide0-0-0,readonly=on -device
ide-cd,bus=ide.0,unit=0,drive=drive-ide0-0-0,id=ide0-0-0 -netdev
tap,fd=34,id=hostnet0 -device
e1000,netdev=hostnet0,id=net0,mac=52:54:00:06:db:55,bus=pci.0,addr=0xa
-chardev pty,id=charserial0 -device
isa-serial,chardev=charserial0,id=serial0 -chardev
socket,id=charchannel0,fd=35,server,nowait -device
virtserialport,bus=virtio-serial0.0,nr=1,chardev=charchannel0,id=channel0,name=org.qemu.guest_agent.0
-chardev spicevmc,id=charchannel1,name=vdagent -device
virtserialport,bus=virtio-serial0.0,nr=2,chardev=charchannel1,id=channel1,name=com.redhat.spice.0
-device usb-tablet,id=input0,bus=usb.0,port=1 -spice
port=5901,addr=127.0.0.1,disable-ticketing,image-compression=off,seamless-migration=on
-device
qxl-vga,id=video0,ram_size=67108864,vram_size=67108864,vram64_size_mb=0,vgamem_mb=16,max_outputs=1,bus=pci.0,addr=0x2
-device intel-hda,id=sound0,bus=pci.0,addr=0x4 -device
hda-duplex,id=sound0-codec0,bus=sound0.0,cad=0 -chardev
spicevmc,id=charredir0,name=usbredir -device
usb-redir,chardev=charredir0,id=redir0,bus=usb.0,port=2 -chardev
spicevmc,id=charredir1,name=usbredir -device
usb-redir,chardev=charredir1,id=redir1,bus=usb.0,port=3 -device
virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x8 -object
rng-random,id=objrng0,filename=/dev/urandom -device
virtio-rng-pci,rng=objrng0,id=rng0,bus=pci.0,addr=0x9 -sandbox
on,obsolete=deny,elevateprivileges=deny,spawn=deny,resourcecontrol=deny
-msg timestamp=on
VM start takes longer that qemu. Any thoughts?? Why is prealloc=yes default
on for nvdimm? Any other important deltas?
On Mon, Sep 2, 2019 at 12:21 PM Michal Privoznik <mprivozn(a)redhat.com>
wrote:
On 8/31/19 7:33 PM, Seema Pandit wrote:
> Hi Michal,
> Thank you for the reply.
> I was having issues compiling qemu code on fedora29. So instead of
dropping
> prealloc in virsh, tried adding prealloc=yes in qemu command line.
> prealloc=yes works. It does not lead to using more system memory when
using
> DAX.
> +Dan
> Here are the steps:
>
> ndctl create-namespace -t pmem -m fsdax --align=4k -s 400G
>
> mkfs.ext4 /dev/pmem0
>
> mount -o dax /dev/pmem0 /mnt/pmem0
>
> dd if=/dev/zero of=/mnt/pmem0/file1 bs=4k count=104857600
>
> [root@system-name]# dd if=/dev/zero of=/mnt/pmem0/file1 bs=4k
> count=104857600
>
> dd: error writing '/mnt/pmem0/file1': No space left on device
>
> 101313980+0 records in
>
> 101313979+0 records out
>
> 414982057984 bytes (415 GB, 386 GiB) copied, 946.495 s, 438 MB/s
>
>
> Slightly smaller file is created than asked.
>
> [root@system-name]# du -sh
>
> 387G .
>
>
> sample qemu command line which works:
>
> qemu-system-x86_64 \
>
> -name test \
>
> -drive
>
file=/var/lib/libvirt/images/test-ad.qcow2,format=qcow2,index=0,media=disk
> \ -m 2G,slots=4,maxmem=428G \ -smp 2 \ -machine pc,accel=kvm,nvdimm=on \
> -enable-kvm \ -object
>
memory-backend-file,id=pmem1,prealloc=yes,share=on,mem-path=/mnt/pmem0/file1,size=386G,align=4K
> \ -device nvdimm,memdev=pmem1,id=nv1 \ -daemonize
Looks like the only difference to the cmd line generated by libvirt and
this one then is align=4K. To confirm that, can you share the full qemu
cmd line as generated by libvirt please?
Libvirt does not do anything special with guest memory, so this is
matter of qemu cmd line and that's why we need to see what's different,
what works and what doesn't. Then we have some lead to understand the
problem IMO.
Michal
11:23 p.m.
On Mon, Sep 2, 2019 at 10:10 AM Seema Pandit <pan.blr.17(a)gmail.com> wrote:
After adding the memoryBacking tag in xml as below (in addition, to other xml changes to
add nvdimm), virsh could allocate AD memory larger than the system RAM and VMs could start
successfully.
<memoryBacking>
<access mode='shared'/>
<discard/>
</memoryBacking>
This adds share=yes in command line.
-object
memory-backend-file,id=memnvdimm0,prealloc=yes,mem-path=/mnt/pmem0/file1,share=yes,size=414464344064
-device nvdimm,node=0,label-size=131072,memdev=memnvdimm0,id=nvdimm0,slot=0
For reference qemu command line where VM starts quickly:
qemu-system-x86_64 \
-name qemu-gold29 \
-drive file=/var/lib/libvirt/images/gold29-ad.qcow2,format=qcow2,index=0,media=disk \ -m
2G,slots=4,maxmem=428G \ -smp 2 \ -machine pc,accel=kvm,nvdimm=on \ -enable-kvm \ -object
memory-backend-file,id=pmem1,share=on,mem-path=/mnt/pmem0/file1,size=386G,align=4K \
-device nvdimm,memdev=pmem1,id=nv1 \ -daemonize
Qemu command line generated from virsh: (please note VM now starts with this command
line, shared=yes.)
/usr/bin/qemu-system-x86_64 -machine accel=kvm -name guest=mix-test,debug-threads=on -S
-object
secret,id=masterKey0,format=raw,file=/var/lib/libvirt/qemu/domain-18-mix-test/master-key.aes
-machine pc-i440fx-3.0,accel=kvm,usb=off,vmport=off,dump-guest-core=off,nvdimm=on -cpu
Skylake-Server-IBRS,hypervisor=on -m size=2097152k,slots=16,maxmem=419430400k -realtime
mlock=off -smp 2,sockets=2,cores=1,threads=1 -object
memory-backend-file,id=ram-node0,mem-path=/var/lib/libvirt/qem
/ram/libvirt/qemu/18-mix-test/ram-node0,discard-data=yes,share=yes,size=2147483648 -numa
node,nodeid=0,cpus=0-1,memdev=ram-node0 -object
memory-backend-file,id=memnvdimm0,prealloc=yes,mem-path=/mnt/pmem0/file1,share=yes,size=414464344064
-device nvdimm,node=0,label-size=131072,memdev=memnvdimm0,id=nvdimm0,slot=0 -uuid
318c0529-0330-460b-8d0a-3b253e9decdd -no-user-config -nodefaults -chardev
socket,id=charmonitor,fd=32,server,nowait -mon chardev=charmonitor,id=monitor,mode=control
-rtc base=utc,driftfix=slew -global kvm-pit.lost_tick_policy=delay -no-hpet -no-shutdown
-global PIIX4_PM.disable_s3=1 -global PIIX4_PM.disable_s4=1 -boot strict=on -device
ich9-usb-ehci1,id=usb,bus=pci.0,addr=0x5.0x7 -device
ich9-usb-uhci1,masterbus=usb.0,firstport=0,bus=pci.0,multifunction=on,addr=0x5 -device
ich9-usb-uhci2,masterbus=usb.0,firstport=2,bus=pci.0,addr=0x5.0x1 -device
ich9-usb-uhci3,masterbus=usb.0,firstport=4,bus=pci.0,addr=0x5.0x2 -device
virtio-serial-pci,id=virtio-serial0,bus=pci.0,addr=0x6 -drive
file=/var/lib/libvirt/images/mix-test.qcow2,format=qcow2,if=none,id=drive-virtio-disk0
-device
virtio-blk-pci,scsi=off,bus=pci.0,addr=0x7,drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1
-drive if=none,id=drive-ide0-0-0,readonly=on -device
ide-cd,bus=ide.0,unit=0,drive=drive-ide0-0-0,id=ide0-0-0 -netdev tap,fd=34,id=hostnet0
-device e1000,netdev=hostnet0,id=net0,mac=52:54:00:06:db:55,bus=pci.0,addr=0xa -chardev
pty,id=charserial0 -device isa-serial,chardev=charserial0,id=serial0 -chardev
socket,id=charchannel0,fd=35,server,nowait -device
virtserialport,bus=virtio-serial0.0,nr=1,chardev=charchannel0,id=channel0,name=org.qemu.guest_agent.0
-chardev spicevmc,id=charchannel1,name=vdagent -device
virtserialport,bus=virtio-serial0.0,nr=2,chardev=charchannel1,id=channel1,name=com.redhat.spice.0
-device usb-tablet,id=input0,bus=usb.0,port=1 -spice
port=5901,addr=127.0.0.1,disable-ticketing,image-compression=off,seamless-migration=on
-device
qxl-vga,id=video0,ram_size=67108864,vram_size=67108864,vram64_size_mb=0,vgamem_mb=16,max_outputs=1,bus=pci.0,addr=0x2
-device intel-hda,id=sound0,bus=pci.0,addr=0x4 -device
hda-duplex,id=sound0-codec0,bus=sound0.0,cad=0 -chardev
spicevmc,id=charredir0,name=usbredir -device
usb-redir,chardev=charredir0,id=redir0,bus=usb.0,port=2 -chardev
spicevmc,id=charredir1,name=usbredir -device
usb-redir,chardev=charredir1,id=redir1,bus=usb.0,port=3 -device
virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x8 -object
rng-random,id=objrng0,filename=/dev/urandom -device
virtio-rng-pci,rng=objrng0,id=rng0,bus=pci.0,addr=0x9 -sandbox
on,obsolete=deny,elevateprivileges=deny,spawn=deny,resourcecontrol=deny -msg timestamp=on
VM start takes longer that qemu. Any thoughts?? Why is prealloc=yes default on for
nvdimm? Any other important deltas?
The "prealloc" option is a "pay me now" vs "pay me later"
type of
decision. If the guest workload is ok to absorb fault latency at run
time then disable prealloc, if it would prefer more predictable
latency and pay all the fault penalty up front then specify prealloc.
The "shared" parameter, if it means MAP_SHARED vs MAP_PRIVATE, must be
set to "yes" if the guest expects persistence. MAP_PRIVATE is
otherwise unacceptable for emulating persistent memory because writes
to private memory are discarded, and as you have seen require volatile
DRAM backing even in the DAX case.
2:56 a.m.
Actually there is still some issue around this. When trying to start
another VM, so using even more pmem, there is a different issue now. Error
copied below.
[]# virsh start manual_clone
error: Failed to start domain manual_clone
error: internal error: qemu unexpectedly closed the monitor: ftruncate:
Invalid argument
2019-09-03T21:28:41.031924Z qemu-system-x86_64: -object
memory-backend-file,id=memnvdimm0,prealloc=yes,mem-path=/dev/dax1.1,share=yes,size=73014444032:
os_mem_prealloc: Insufficient free host memory pages available to allocate
guest RAM
Old error was
Error:
# virsh start test
error: Failed to start domain test
error: internal error: qemu unexpectedly closed the monitor: ftruncate:
Invalid argument 2019-08-22T04:16:08.744402Z qemu-system-x86_64: -object
memory-backend-file,id=memnvdimm0,prealloc=yes,mem-path=/dev/dax1.0,size=403726925824:
unable to map backing store for guest RAM: Cannot allocate memory
On Tue, Sep 3, 2019 at 9:53 AM Dan Williams <dan.j.williams(a)intel.com>
wrote:
On Mon, Sep 2, 2019 at 10:10 AM Seema Pandit
<pan.blr.17(a)gmail.com> wrote:
>
> After adding the memoryBacking tag in xml as below (in addition, to
other xml changes to add nvdimm), virsh could allocate AD memory larger
than the system RAM and VMs could start successfully.
>
> <memoryBacking>
>
> <access mode='shared'/>
>
> <discard/>
>
> </memoryBacking>
>
>
>
> This adds share=yes in command line.
>
>
>
> -object
memory-backend-file,id=memnvdimm0,prealloc=yes,mem-path=/mnt/pmem0/file1,share=yes,size=414464344064
-device nvdimm,node=0,label-size=131072,memdev=memnvdimm0,id=nvdimm0,slot=0
>
>
>
>
>
> For reference qemu command line where VM starts quickly:
>
> qemu-system-x86_64 \
>
> -name qemu-gold29 \
>
> -drive
file=/var/lib/libvirt/images/gold29-ad.qcow2,format=qcow2,index=0,media=disk
\ -m 2G,slots=4,maxmem=428G \ -smp 2 \ -machine pc,accel=kvm,nvdimm=on \
-enable-kvm \ -object
memory-backend-file,id=pmem1,share=on,mem-path=/mnt/pmem0/file1,size=386G,align=4K
\ -device nvdimm,memdev=pmem1,id=nv1 \ -daemonize
>
>
>
>
>
> Qemu command line generated from virsh: (please note VM now starts with
this command line, shared=yes.)
>
>
>
> /usr/bin/qemu-system-x86_64 -machine accel=kvm -name
guest=mix-test,debug-threads=on -S -object
secret,id=masterKey0,format=raw,file=/var/lib/libvirt/qemu/domain-18-mix-test/master-key.aes
-machine
pc-i440fx-3.0,accel=kvm,usb=off,vmport=off,dump-guest-core=off,nvdimm=on
-cpu Skylake-Server-IBRS,hypervisor=on -m
size=2097152k,slots=16,maxmem=419430400k -realtime mlock=off -smp
2,sockets=2,cores=1,threads=1 -object
memory-backend-file,id=ram-node0,mem-path=/var/lib/libvirt/qem
/ram/libvirt/qemu/18-mix-test/ram-node0,discard-data=yes,share=yes,size=2147483648
-numa node,nodeid=0,cpus=0-1,memdev=ram-node0 -object
memory-backend-file,id=memnvdimm0,prealloc=yes,mem-path=/mnt/pmem0/file1,share=yes,size=414464344064
-device nvdimm,node=0,label-size=131072,memdev=memnvdimm0,id=nvdimm0,slot=0
-uuid 318c0529-0330-460b-8d0a-3b253e9decdd -no-user-config -nodefaults
-chardev socket,id=charmonitor,fd=32,server,nowait -mon
chardev=charmonitor,id=monitor,mode=control -rtc base=utc,driftfix=slew
-global kvm-pit.lost_tick_policy=delay -no-hpet -no-shutdown -global
PIIX4_PM.disable_s3=1 -global PIIX4_PM.disable_s4=1 -boot strict=on -device
ich9-usb-ehci1,id=usb,bus=pci.0,addr=0x5.0x7 -device
ich9-usb-uhci1,masterbus=usb.0,firstport=0,bus=pci.0,multifunction=on,addr=0x5
-device ich9-usb-uhci2,masterbus=usb.0,firstport=2,bus=pci.0,addr=0x5.0x1
-device ich9-usb-uhci3,masterbus=usb.0,firstport=4,bus=pci.0,addr=0x5.0x2
-device virtio-serial-pci,id=virtio-serial0,bus=pci.0,addr=0x6 -drive
file=/var/lib/libvirt/images/mix-test.qcow2,format=qcow2,if=none,id=drive-virtio-disk0
-device
virtio-blk-pci,scsi=off,bus=pci.0,addr=0x7,drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1
-drive if=none,id=drive-ide0-0-0,readonly=on -device
ide-cd,bus=ide.0,unit=0,drive=drive-ide0-0-0,id=ide0-0-0 -netdev
tap,fd=34,id=hostnet0 -device
e1000,netdev=hostnet0,id=net0,mac=52:54:00:06:db:55,bus=pci.0,addr=0xa
-chardev pty,id=charserial0 -device
isa-serial,chardev=charserial0,id=serial0 -chardev
socket,id=charchannel0,fd=35,server,nowait -device
virtserialport,bus=virtio-serial0.0,nr=1,chardev=charchannel0,id=channel0,name=org.qemu.guest_agent.0
-chardev spicevmc,id=charchannel1,name=vdagent -device
virtserialport,bus=virtio-serial0.0,nr=2,chardev=charchannel1,id=channel1,name=com.redhat.spice.0
-device usb-tablet,id=input0,bus=usb.0,port=1 -spice
port=5901,addr=127.0.0.1,disable-ticketing,image-compression=off,seamless-migration=on
-device
qxl-vga,id=video0,ram_size=67108864,vram_size=67108864,vram64_size_mb=0,vgamem_mb=16,max_outputs=1,bus=pci.0,addr=0x2
-device intel-hda,id=sound0,bus=pci.0,addr=0x4 -device
hda-duplex,id=sound0-codec0,bus=sound0.0,cad=0 -chardev
spicevmc,id=charredir0,name=usbredir -device
usb-redir,chardev=charredir0,id=redir0,bus=usb.0,port=2 -chardev
spicevmc,id=charredir1,name=usbredir -device
usb-redir,chardev=charredir1,id=redir1,bus=usb.0,port=3 -device
virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x8 -object
rng-random,id=objrng0,filename=/dev/urandom -device
virtio-rng-pci,rng=objrng0,id=rng0,bus=pci.0,addr=0x9 -sandbox
on,obsolete=deny,elevateprivileges=deny,spawn=deny,resourcecontrol=deny
-msg timestamp=on
>
>
> VM start takes longer that qemu. Any thoughts?? Why is prealloc=yes
default on for nvdimm? Any other important deltas?
>
The "prealloc" option is a "pay me now" vs "pay me later"
type of
decision. If the guest workload is ok to absorb fault latency at run
time then disable prealloc, if it would prefer more predictable
latency and pay all the fault penalty up front then specify prealloc.
The "shared" parameter, if it means MAP_SHARED vs MAP_PRIVATE, must be
set to "yes" if the guest expects persistence. MAP_PRIVATE is
otherwise unacceptable for emulating persistent memory because writes
to private memory are discarded, and as you have seen require volatile
DRAM backing even in the DAX case.
11:31 a.m.
On Wed, Sep 4, 2019 at 12:56 AM Seema Pandit <pan.blr.17(a)gmail.com> wrote:
Actually there is still some issue around this. When trying to start another VM, so using
even more pmem, there is a different issue now. Error copied below.
[]# virsh start manual_clone
error: Failed to start domain manual_clone
error: internal error: qemu unexpectedly closed the monitor: ftruncate: Invalid argument
2019-09-03T21:28:41.031924Z qemu-system-x86_64: -object
memory-backend-file,id=memnvdimm0,prealloc=yes,mem-path=/dev/dax1.1,share=yes,size=73014444032:
os_mem_prealloc: Insufficient free host memory pages available to allocate guest RAM
/dev/dax instances do not support the ftruncate syscall, and
device-dax instances are already fully allocated by definition. The
prealloc option is simply invalid for /dev/dax targets.
12:43 p.m.
On 9/4/19 6:31 PM, Dan Williams wrote:
On Wed, Sep 4, 2019 at 12:56 AM Seema Pandit
<pan.blr.17(a)gmail.com> wrote:
>
> Actually there is still some issue around this. When trying to start another VM, so
using even more pmem, there is a different issue now. Error copied below.
>
> []# virsh start manual_clone
>
> error: Failed to start domain manual_clone
>
> error: internal error: qemu unexpectedly closed the monitor: ftruncate: Invalid
argument
>
> 2019-09-03T21:28:41.031924Z qemu-system-x86_64: -object
memory-backend-file,id=memnvdimm0,prealloc=yes,mem-path=/dev/dax1.1,share=yes,size=73014444032:
os_mem_prealloc: Insufficient free host memory pages available to allocate guest RAM
/dev/dax instances do not support the ftruncate syscall, and
device-dax instances are already fully allocated by definition. The
prealloc option is simply invalid for /dev/dax targets.
Ah, in that case we need an XML knob that if set doesn't put
prealloc=yes onto the qemu cmd line. Unfortunatelly, I don't think I
have any spare time to implement that, so please be my guest.
Michal
1900
days inactive
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days old
8 comments
4 participants
participants (4)
-
Dan Williams -
Michal Privoznik -
Michal Prívozník
-
Seema Pandit