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SubjectRe: [PATCH] virtio_balloon: Fix endless deflation and inflation on arm64
From
On 8/29/23 11:54, Gavin Shan wrote:
> The deflation request to the target, which isn't unaligned to the
> guest page size causes endless deflation and inflation actions. For
> example, we receive the flooding QMP events for the changes on memory
> balloon's size after a deflation request to the unaligned target is
> sent for the ARM64 guest, where we have 64KB base page size.
>
> /home/gavin/sandbox/qemu.main/build/qemu-system-aarch64 \
> -accel kvm -machine virt,gic-version=host -cpu host \
> -smp maxcpus=8,cpus=8,sockets=2,clusters=2,cores=2,threads=1 \
> -m 1024M,slots=16,maxmem=64G \
> -object memory-backend-ram,id=mem0,size=512M \
> -object memory-backend-ram,id=mem1,size=512M \
> -numa node,nodeid=0,memdev=mem0,cpus=0-3 \
> -numa node,nodeid=1,memdev=mem1,cpus=4-7 \
> : \
> -device virtio-balloon-pci,id=balloon0,bus=pcie.10
>
> { "execute" : "balloon", "arguments": { "value" : 1073672192 } }
> {"return": {}}
> {"timestamp": {"seconds": 1693272173, "microseconds": 88667}, \
> "event": "BALLOON_CHANGE", "data": {"actual": 1073610752}}
> {"timestamp": {"seconds": 1693272174, "microseconds": 89704}, \
> "event": "BALLOON_CHANGE", "data": {"actual": 1073610752}}
> {"timestamp": {"seconds": 1693272175, "microseconds": 90819}, \
> "event": "BALLOON_CHANGE", "data": {"actual": 1073610752}}
> {"timestamp": {"seconds": 1693272176, "microseconds": 91961}, \
> "event": "BALLOON_CHANGE", "data": {"actual": 1073610752}}
> {"timestamp": {"seconds": 1693272177, "microseconds": 93040}, \
> "event": "BALLOON_CHANGE", "data": {"actual": 1073676288}}
> {"timestamp": {"seconds": 1693272178, "microseconds": 94117}, \
> "event": "BALLOON_CHANGE", "data": {"actual": 1073676288}}
> {"timestamp": {"seconds": 1693272179, "microseconds": 95337}, \
> "event": "BALLOON_CHANGE", "data": {"actual": 1073610752}}
> {"timestamp": {"seconds": 1693272180, "microseconds": 96615}, \
> "event": "BALLOON_CHANGE", "data": {"actual": 1073676288}}
> {"timestamp": {"seconds": 1693272181, "microseconds": 97626}, \
> "event": "BALLOON_CHANGE", "data": {"actual": 1073610752}}
> {"timestamp": {"seconds": 1693272182, "microseconds": 98693}, \
> "event": "BALLOON_CHANGE", "data": {"actual": 1073676288}}
> {"timestamp": {"seconds": 1693272183, "microseconds": 99698}, \
> "event": "BALLOON_CHANGE", "data": {"actual": 1073610752}}
> {"timestamp": {"seconds": 1693272184, "microseconds": 100727}, \
> "event": "BALLOON_CHANGE", "data": {"actual": 1073610752}}
> {"timestamp": {"seconds": 1693272185, "microseconds": 90430}, \
> "event": "BALLOON_CHANGE", "data": {"actual": 1073610752}}
> {"timestamp": {"seconds": 1693272186, "microseconds": 102999}, \
> "event": "BALLOON_CHANGE", "data": {"actual": 1073676288}}
> :
> <The similar QMP events repeat>
>
> Fix it by having the target aligned to the guest page size, 64KB
> in this specific case. With this applied, no flooding QMP event
> is observed and the memory balloon's size can be stablizied to
> 0x3ffe0000 soon after the deflation request is sent.
>
> { "execute" : "balloon", "arguments": { "value" : 1073672192 } }
> {"return": {}}
> {"timestamp": {"seconds": 1693273328, "microseconds": 793075}, \
> "event": "BALLOON_CHANGE", "data": {"actual": 1073610752}}
> { "execute" : "query-balloon" }
> {"return": {"actual": 1073610752}}
>
> Signed-off-by: Gavin Shan <gshan@redhat.com>
> ---
> drivers/virtio/virtio_balloon.c | 13 ++++++++++++-
> 1 file changed, 12 insertions(+), 1 deletion(-)
>

It was supposed to copy David, Jason and Zhenyu. I don't know how they have been
missed. My script may run into problems temporarily. Amending for it.

Thanks,
Gavin

> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 5b15936a5214..625caac35264 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -386,6 +386,17 @@ static void stats_handle_request(struct virtio_balloon *vb)
> virtqueue_kick(vq);
> }
>
> +static inline s64 align_pages_up(s64 diff)
> +{
> + if (diff == 0)
> + return diff;
> +
> + if (diff > 0)
> + return ALIGN(diff, VIRTIO_BALLOON_PAGES_PER_PAGE);
> +
> + return -ALIGN(-diff, VIRTIO_BALLOON_PAGES_PER_PAGE);
> +}
> +
> static inline s64 towards_target(struct virtio_balloon *vb)
> {
> s64 target;
> @@ -396,7 +407,7 @@ static inline s64 towards_target(struct virtio_balloon *vb)
> &num_pages);
>
> target = num_pages;
> - return target - vb->num_pages;
> + return align_pages_up(target - vb->num_pages);
> }
>
> /* Gives back @num_to_return blocks of free pages to mm. */

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