Hai: Do we know much about what lives in the big 1G huge pages? Are they mostly static or are they changing reasonably frequently?

First version of qemu posted to qemu-devel; note this supports 2MB hugepages but not 1GB. 

1GB support is not currently reasonable with the technique we're using in the kernel.

Fixed in 2.9
Merged as part of 251501a3714096f807778f6d3f03711dcdb9ce29

      postcopy: Add extra check for COPY function
      postcopy: Add doc about hugepages and postcopy
      postcopy: Check for userfault+hugepage feature
      postcopy: Update userfaultfd.h header
      postcopy: Allow hugepages
      postcopy: Send whole huge pages
      postcopy: Mask fault addresses to huge page boundary
      postcopy: Load huge pages in one go
      postcopy: Use temporary for placing zero huge pages
      postcopy: Plumb pagesize down into place helpers
      postcopy: Record largest page size
      postcopy: enhance ram_block_discard_range for hugepages
      exec: ram_block_discard_range
      postcopy: Chunk discards for hugepages
      postcopy: Transmit and compare individual page sizes
      postcopy: Transmit ram size summary word

This bug is fixed for qemu-kvm-rhev-2.9.0-1.el7
Bug verify:
Version:
3.10.0-657.el7.x86_64
qemu-kvm-rhev-2.9.0-1.el7.x86_64
seabios-bin-1.10.2-2.el7.noarch

Steps:
1)Configure hugepage in src host and dst host
# echo 2048 > /proc/sys/vm/nr_hugepages
# cat /proc/meminfo | grep -i hugepage
AnonHugePages:     14336 kB
HugePages_Total:    2048
HugePages_Free:     2048
HugePages_Rsvd:        0
HugePages_Surp:        0
Hugepagesize:       2048 kB
2)Boot a guest on src host with qemu cli:
/usr/libexec/qemu-kvm \
    -name 'vm1'  \
    -sandbox off  \
    -machine pc-i440fx-rhel7.4.0 \
    -nodefaults  \
    -device virtio-serial-pci,id=virtio_serial_pci0,bus=pci.0,addr=04 \
    -device usb-ehci,id=usb1,bus=pci.0,addr=06 \
    -device virtio-scsi-pci,id=virtio_scsi_pci0,bus=pci.0,addr=09 \
    -drive id=drive_image1,if=none,snapshot=off,aio=threads,cache=unsafe,format=qcow2,file=/root/rhel74-64-virtio.qcow2 \
    -device virtio-blk-pci,id=image1,drive=drive_image1,bus=pci.0,bootindex=0 \
    -device virtio-net-pci,mac=9a:4f:50:51:52:53,id=id9HRc5V,vectors=4,netdev=idjlQN53,bus=pci.0  \
    -netdev tap,id=idjlQN53,vhost=off,script=/etc/qemu-ifup,downscript=/etc/qemu-ifdown \
    -mem-path /dev/hugepages \
    -mem-prealloc \
    -m 4096 \
    -smp 4 \
    -device usb-tablet,id=usb-tablet1,bus=usb1.0,port=1  \
    -device usb-mouse,id=input1,bus=usb1.0,port=2 \
    -device usb-kbd,id=input2,bus=usb1.0,port=3 \
    -vnc :1 \
    -qmp tcp:0:8881,server,nowait \
    -vga std \
    -monitor stdio \
    -rtc base=localtime  \
    -boot order=cdn,once=n,menu=on,strict=off  \
    -enable-kvm  \
    -watchdog i6300esb \
    -watchdog-action reset \
    -device virtio-balloon-pci,id=balloon0,bus=pci.0 
3)Launch a guest in dst host for listening mode with "-incoming tcp:0:5801" 
4)In guest, execute program to generate dirty page
# cat test.c 
#include <stdlib.h>
#include <stdio.h>
#include <signal.h>
int main()
{
void wakeup();
signal(SIGALRM,wakeup);
alarm(120);
char *buf = (char *) calloc(40960, 4096);
while (1) {
int i;
for (i = 0; i < 40960 * 4; i++) {
buf[i * 4096 / 4]++;
}
printf(".");
}
}
void wakeup()
{
exit(0);
}
# gcc test.c -o test
# ./test
5)In src host, do migration and enable postcopy, after generating dirty page, switch to postcopy mode
(qemu) migrate_set_capability postcopy-ram on
(qemu) migrate -d tcp:10.16.184.92:5801
(qemu) info migrate
capabilities: xbzrle: off rdma-pin-all: off auto-converge: off zero-blocks: off compress: off events: off postcopy-ram: on x-colo: off release-ram: off 
Migration status: active 
dirty sync count: 3
dirty pages rate: 6889 pages
(qemu) migrate_start_postcopy 

Actual result:
Postcopy migration completed and vm works well.
Src host:
(qemu) info migrate
capabilities: xbzrle: off rdma-pin-all: off auto-converge: off zero-blocks: off compress: off events: off postcopy-ram: on x-colo: off release-ram: off 
Migration status: completed
dirty sync count: 6
postcopy request count: 268
Dst host:
(qemu) info status 
VM status: running

So, this bug is fixed.

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHSA-2017:2392

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHSA-2017:2392

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHSA-2017:2392

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHSA-2017:2392

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHSA-2017:2392

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHSA-2017:2392