On Thu, Jan 7, 2016 at 1:19 PM, zhanghailiang <zhang.zhanghaili...@huawei.com> wrote: > For now, we still didn't support live memory snapshot, we have discussed > a scheme which based on userfaultfd long time ago. > You can find the discussion by the follow link: > https://lists.nongnu.org/archive/html/qemu-devel/2014-11/msg01779.html > > The scheme is based on userfaultfd's write-protect capability. > The userfaultfd write protection feature is available here: > http://www.spinics.net/lists/linux-mm/msg97422.html > > The process of this live memory scheme is like bellow: > 1. Pause VM > 2. Enable write-protect fault notification by using userfaultfd to > mark VM's memory to write-protect (readonly). > 3. Save VM's static state (here is device state) to snapshot file > 4. Resume VM, VM is going to run. > 5. Snapshot thread begins to save VM's live state (here is RAM) into > snapshot file. > 6. During this time, all the actions of writing VM's memory will be blocked > by kernel, and kernel will wakeup the fault treating thread in qemu to > process this write-protect fault. The fault treating thread will deliver > this > page's address to snapshot thread. > 7. snapshot thread gets this address, save this page into snasphot file, > and then remove the write-protect by using userfaultfd API, after that, > the actions of writing will be recovered. > 8. Repeat step 5~7 until all VM's memory is saved to snapshot file > > Compared with the feature of 'migrate VM's state to file', > the main difference for live memory snapshot is it has little time delay for > catching VM's state. It just captures the VM's state while got users snapshot > command, just like take a photo of VM's state. > > For now, we only support tcg accelerator, since userfaultfd is not supporting > tracking write faults for KVM. > > Usage: > 1. Take a snapshot > #x86_64-softmmu/qemu-system-x86_64 -machine pc-i440fx-2.5,accel=tcg,usb=off > -drive > file=/mnt/windows/win7_install.qcow2.bak,if=none,id=drive-ide0-0-1,format=qcow2,cache=none > -device ide-hd,bus=ide.0,unit=1,drive=drive-ide0-0-1,id=ide0-0-1 -vnc :7 -m > 8192 -smp 1 -netdev tap,id=bn0 -device virtio-net-pci,id=net-pci0,netdev=bn0 > --monitor stdio > Issue snapshot command: > (qemu)migrate -d file:/home/Snapshot > 2. Revert to the snapshot > #x86_64-softmmu/qemu-system-x86_64 -machine pc-i440fx-2.5,accel=tcg,usb=off > -drive > file=/mnt/windows/win7_install.qcow2.bak,if=none,id=drive-ide0-0-1,format=qcow2,cache=none > -device ide-hd,bus=ide.0,unit=1,drive=drive-ide0-0-1,id=ide0-0-1 -vnc :7 -m > 8192 -smp 1 -netdev tap,id=bn0 -device virtio-net-pci,id=net-pci0,netdev=bn0 > --monitor stdio -incoming file:/home/Snapshot > > NOTE: > The userfaultfd write protection feature does not support THP for now, > Before taking snapshot, please disable THP by: > echo never > /sys/kernel/mm/transparent_hugepage/enabled > > TODO: > - Reduce the influence for VM while taking snapshot > > zhanghailiang (13): > postcopy/migration: Split fault related state into struct > UserfaultState > migration: Allow the migrate command to work on file: urls > migration: Allow -incoming to work on file: urls > migration: Create a snapshot thread to realize saving memory snapshot > migration: implement initialization work for snapshot > QEMUSizedBuffer: Introduce two help functions for qsb > savevm: Split qemu_savevm_state_complete_precopy() into two helper > functions > snapshot: Save VM's device state into snapshot file > migration/postcopy-ram: fix some helper functions to support > userfaultfd write-protect > snapshot: Enable the write-protect notification capability for VM's > RAM > snapshot/migration: Save VM's RAM into snapshot file > migration/ram: Fix some helper functions' parameter to use > PageSearchStatus > snapshot: Remove page's write-protect and copy the content during > setup stage > > include/migration/migration.h | 41 +++++-- > include/migration/postcopy-ram.h | 9 +- > include/migration/qemu-file.h | 3 +- > include/qemu/typedefs.h | 1 + > include/sysemu/sysemu.h | 3 + > linux-headers/linux/userfaultfd.h | 21 +++- > migration/fd.c | 51 ++++++++- > migration/migration.c | 101 ++++++++++++++++- > migration/postcopy-ram.c | 229 > ++++++++++++++++++++++++++++---------- > migration/qemu-file-buf.c | 61 ++++++++++ > migration/ram.c | 104 ++++++++++++----- > migration/savevm.c | 90 ++++++++++++--- > trace-events | 1 + > 13 files changed, 587 insertions(+), 128 deletions(-) > > -- > 1.8.3.1 > > >
Hi Hailiang, Can I get the status of this patch series ? I cannot find a v2. About TCG limitation, is KVM support on a TODO list or is there a strong technical barrier ? Thanks, Baptiste
