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

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Message-Id: <0661b05a-d9d0-d374-44e8-2583463e94c2@de.ibm.com>
Date:   Thu, 27 Dec 2018 12:31:11 +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
Subject: Re: [PATCH v37 0/3] Virtio-balloon: support free page reporting

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(-)
>