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

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Date:   Thu, 27 Dec 2018 12:59:04 +0100
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     Wei Wang <wei.w.wang@...el.com>, virtio-dev@...ts.oasis-open.org,
        linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
        linux-mm@...ck.org, mst@...hat.com, mhocko@...nel.org,
        akpm@...ux-foundation.org, dgilbert@...hat.com
Cc:     torvalds@...ux-foundation.org, pbonzini@...hat.com,
        liliang.opensource@...il.com, yang.zhang.wz@...il.com,
        quan.xu0@...il.com, nilal@...hat.com, riel@...hat.com,
        peterx@...hat.com, quintela@...hat.com,
        Halil Pasic <pasic@...ux.ibm.com>,
        Cornelia Huck <cohuck@...hat.com>
Subject: Re: [PATCH v37 0/3] Virtio-balloon: support free page reporting

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(-)
>>