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Bug 1703765 - [RHEL7] QEMU dies unhappy death if nr of huge page is zero.
Summary: [RHEL7] QEMU dies unhappy death if nr of huge page is zero.
Keywords:
Status: CLOSED WONTFIX
Alias: None
Product: Red Hat Enterprise Linux 7
Classification: Red Hat
Component: qemu-kvm-rhev
Version: 7.7
Hardware: ppc64le
OS: Unspecified
medium
medium
Target Milestone: rc
: ---
Assignee: David Gibson
QA Contact: Min Deng
URL:
Whiteboard:
Depends On: 1686261
Blocks:
TreeView+ depends on / blocked
 
Reported: 2019-04-28 07:59 UTC by Min Deng
Modified: 2019-12-02 07:49 UTC (History)
8 users (show)

Fixed In Version:
Doc Type: If docs needed, set a value
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Clone Of:
Environment:
Last Closed: 2019-05-23 01:35:55 UTC
Target Upstream Version:
Embargoed:

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Description Min Deng 2019-04-28 07:59:37 UTC 
Description of problem:
[RHEL7]QEMU dies unhappy death if nr of huge page is zero. 

Version-Release number of selected component (if applicable):
kernel-3.10.0-1037.el7.ppc64le
qemu-kvm-rhev-2.12.0-26.el7.ppc64le

How reproducible:
3/3

Steps to Reproduce:
1.Configure huge page on P8 host
  mkdir /dev/hugepages
  mount -t hugetlbfs -o pagesize=16M none /dev/hugepages
  echo 15000 > /proc/sys/vm/nr_hugepages
  echo 0 > /sys/devices/system/node/node0/hugepages/hugepages-16384kB/nr_hugepages
  [root@ibm-p8-kvm-02-qe runs]# cat /sys/devices/system/node/node*/meminfo | fgrep Huge
  Node 0 AnonHugePages:         0 kB
  Node 0 HugePages_Total:     0
  Node 0 HugePages_Free:      0
  Node 0 HugePages_Surp:      0

2.Bind guest's memory on numa node 0 
numactl --membind=0 numactl --membind=0 /usr/libexec/qemu-kvm -name avocado-vt-vm1 -machine pseries,max-cpu-compat=power8 -nodefaults -device VGA,bus=pci.0,addr=0x2 -chardev socket,id=serial_id_serial0,path=/tmp/5,server,nowait -device spapr-vty,reg=0x30000000,chardev=serial_id_serial0 -device qemu-xhci,id=usb1,bus=pci.0,addr=0x3 -device virtio-scsi-pci,id=virtio_scsi_pci0,bus=pci.0,addr=0x4 -device scsi-hd,id=image1,drive=drive_scsi11,bus=virtio_scsi_pci0.0,channel=0,scsi-id=0,lun=0,bootindex=0 -blockdev driver=file,cache.direct=on,cache.no-flush=off,filename=rhel76-ppc64-virtio-scsi.qcow2,node-name=drive_scsi1 -blockdev driver=qcow2,node-name=drive_scsi11,file=drive_scsi1 -m 1G,slots=256,maxmem=2T -mem-path /dev/hugepages -smp 2,maxcpus=2,cores=1,threads=1,sockets=2 -monitor stdio

Actual results:
QEMU 2.12.0 monitor - type 'help' for more information
(qemu) Bus error
and QEMU quits finally

Expected results:
It's an extreme situation,whatever it is not a good result for QEMU dies such unhappy death.

Additional info
Probably,the below result should be preferred.

1.Inadequate huge pages were set unfortunately before booting up a guest
 
[root@ibm-p8-rhevm-07 mdeng]# cat /proc/meminfo|grep Huge
AnonHugePages:         0 kB
HugePages_Total:      10
HugePages_Free:       10
HugePages_Rsvd:        0
HugePages_Surp:        0
Hugepagesize:      16384 kB

2.boot up a guest 
CLI,
...-m 5G -mem-path /mnt/kvm_hugepage -numa node,mem=5G,cpus=0,nodeid=0 -numa node...

QEMU 2.12.0 monitor - type 'help' for more information
(qemu) qemu-kvm: unable to map backing store for guest RAM: Cannot allocate memory
qemu-kvm: falling back to regular RAM allocation.
Comment 2 David Gibson 2019-05-06 04:15:57 UTC 
Min,

Does this problem also occur with RHEL8.0 or RHEL8.1?
Comment 3 Min Deng 2019-05-06 05:07:15 UTC 
Hi David,
   The problem also occurred on rhel8.0.
Thanks.
Min
Comment 4 Min Deng 2019-05-06 05:08:08 UTC 
For your reference,
Bug 1686261 - [RHEL8]QEMU dies unhappy death if nr of huge page is zero.
Comment 5 David Gibson 2019-05-23 01:35:55 UTC 
This is actually pretty difficult to fix in the code, I'm looking at options but it might not be worth the trouble, since this is purely to improve an error message in a case which definitely can't work.

Note that you can workaround this by adding the "-mem-prealloc" option.  With that option qemu will check for available memory earlier and fail with a nicer message.

This definitely isn't severe enough to fix in RHEL7, especially since the code change would need to be quite significant.
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