Re: [PATCH v37 0/3] Virtio-balloon: support free page reporting

[Christian Borntraeger <borntraeger@de.ibm.com>]

This patch triggers random crashes in the guest kernel on s390 early during boot.
No migration and no setting of the balloon is involved.




On 27.08.2018 03:32, Wei Wang wrote:
> The new feature, VIRTIO_BALLOON_F_FREE_PAGE_HINT, implemented by this
> series enables the virtio-balloon driver to report hints of guest free
> pages to host. It can be used to accelerate virtual machine (VM) live
> migration. Here is an introduction of this usage:
> 
> Live migration needs to transfer the VM's memory from the source machine
> to the destination round by round. For the 1st round, all the VM's memory
> is transferred. From the 2nd round, only the pieces of memory that were
> written by the guest (after the 1st round) are transferred. One method
> that is popularly used by the hypervisor to track which part of memory is
> written is to have the hypervisor write-protect all the guest memory.
> 
> This feature enables the optimization by skipping the transfer of guest
> free pages during VM live migration. It is not concerned that the memory
> pages are used after they are given to the hypervisor as a hint of the
> free pages, because they will be tracked by the hypervisor and transferred
> in the subsequent round if they are used and written.
> 
> * Tests
> 1 Test Environment
>     Host: Intel(R) Xeon(R) CPU E5-2699 v4 @ 2.20GHz
>     Migration setup: migrate_set_speed 100G, migrate_set_downtime 400ms
> 
> 2 Test Results (results are averaged over several repeated runs)
>     2.1 Guest setup: 8G RAM, 4 vCPU
>         2.1.1 Idle guest live migration time
>             Optimization v.s. Legacy = 620ms vs 2970ms
>             --> ~79% reduction
>         2.1.2 Guest live migration with Linux compilation workload
>           (i.e. make bzImage -j4) running
>           1) Live Migration Time:
>              Optimization v.s. Legacy = 2273ms v.s. 4502ms
>              --> ~50% reduction
>           2) Linux Compilation Time:
>              Optimization v.s. Legacy = 8min42s v.s. 8min43s
>              --> no obvious difference
> 
>     2.2 Guest setup: 128G RAM, 4 vCPU
>         2.2.1 Idle guest live migration time
>             Optimization v.s. Legacy = 5294ms vs 41651ms
>             --> ~87% reduction
>         2.2.2 Guest live migration with Linux compilation workload
>           1) Live Migration Time:
>             Optimization v.s. Legacy = 8816ms v.s. 54201ms
>             --> 84% reduction
>           2) Linux Compilation Time:
>              Optimization v.s. Legacy = 8min30s v.s. 8min36s
>              --> no obvious difference
> 
> ChangeLog:
> v36->v37:
>     - free the reported pages to mm when receives a DONE cmd from host.
>       Please see patch 1's commit log for reasons. Please see patch 1's
>       commit for detailed explanations.
> 
> For ChangeLogs from v22 to v36, please reference
> https://lkml.org/lkml/2018/7/20/199
> 
> For ChangeLogs before v21, please reference
> https://lwn.net/Articles/743660/
> 
> Wei Wang (3):
>   virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT
>   mm/page_poison: expose page_poisoning_enabled to kernel modules
>   virtio-balloon: VIRTIO_BALLOON_F_PAGE_POISON
> 
>  drivers/virtio/virtio_balloon.c     | 374 ++++++++++++++++++++++++++++++++----
>  include/uapi/linux/virtio_balloon.h |   8 +
>  mm/page_poison.c                    |   6 +
>  3 files changed, 355 insertions(+), 33 deletions(-)
>