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SubjectRe: [PATCH v37 0/3] Virtio-balloon: support free page reporting
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On 27.12.2018 12:31, Christian Borntraeger wrote:
> This patch triggers random crashes in the guest kernel on s390 early during boot.
> No migration and no setting of the balloon is involved.
>

Adding Conny and Halil,

As the QEMU provides no PAGE_HINT feature yet, this quick hack makes the
guest boot fine again:


diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 728ecd1eea305..aa2e1864c5736 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -492,7 +492,7 @@ static int init_vqs(struct virtio_balloon *vb)
callbacks[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL;
}

- err = vb->vdev->config->find_vqs(vb->vdev, VIRTIO_BALLOON_VQ_MAX,
+ err = vb->vdev->config->find_vqs(vb->vdev, 3, //VIRTIO_BALLOON_VQ_MAX,
vqs, callbacks, names, NULL, NULL);
if (err)
return err;

To me it looks like that virtio_ccw_find_vqs will abort if any of the virtqueues
that it is been asked for does not exist (including the earlier ones).


Christian

>
> 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(-)
>>

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