Re: [PATCH v3 2/3] virtio-balloon: improve update_balloon_size_func

[Michael S. Tsirkin]

On Mon, Jan 07, 2019 at 03:01:05PM +0800, Wei Wang wrote:
> There is no need to update the balloon actual register when there is no
> ballooning request. This patch avoids update_balloon_size when diff is 0.
> 
> Signed-off-by: Wei Wang <wei.w.wang@xxxxxxxxx>
> Reviewed-by: Cornelia Huck <cohuck@xxxxxxxxxx>
> Reviewed-by: Halil Pasic <pasic@xxxxxxxxxxxxx>

It sounds reasonable but it does have a side effect of
not writing into actual anymore.

I am not sure actual never can get out of sync as a result.

So better deferred, pls send this in the next merge window.




> ---
>  drivers/virtio/virtio_balloon.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index fb12fe2..e33dc8e 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -457,9 +457,12 @@ static void update_balloon_size_func(struct work_struct *work)
>  			  update_balloon_size_work);
>  	diff = towards_target(vb);
>  
> +	if (!diff)
> +		return;
> +
>  	if (diff > 0)
>  		diff -= fill_balloon(vb, diff);
> -	else if (diff < 0)
> +	else
>  		diff += leak_balloon(vb, -diff);
>  	update_balloon_size(vb);
>  
> -- 
> 2.7.4