linux-kernel - Re: [PATCH v1 2/3] virtio-balloon: deflate up to oom

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Date:   Sun, 22 Oct 2017 06:21:38 +0300
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Wei Wang <wei.w.wang@...el.com>
Cc:     penguin-kernel@...ove.SAKURA.ne.jp, mhocko@...nel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v1 2/3] virtio-balloon: deflate up to oom_pages on OOM

On Fri, Oct 20, 2017 at 07:54:25PM +0800, Wei Wang wrote:
> The current implementation only deflates 256 pages even when a user
> specifies more than that via the oom_pages module param. This patch
> enables the deflating of up to oom_pages pages if there are enough
> inflated pages.
> 
> Signed-off-by: Wei Wang <wei.w.wang@...el.com>
> Cc: Michael S. Tsirkin <mst@...hat.com>
> Cc: Michal Hocko <mhocko@...nel.org>
> Cc: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>

This seems reasonable. Does this by itself help?


> ---
>  drivers/virtio/virtio_balloon.c | 14 +++++++++-----
>  1 file changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 1ecd15a..ab55cf8 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -43,8 +43,8 @@
>  #define OOM_VBALLOON_DEFAULT_PAGES 256
>  #define VIRTBALLOON_OOM_NOTIFY_PRIORITY 80
>  
> -static int oom_pages = OOM_VBALLOON_DEFAULT_PAGES;
> -module_param(oom_pages, int, S_IRUSR | S_IWUSR);
> +static unsigned int oom_pages = OOM_VBALLOON_DEFAULT_PAGES;
> +module_param(oom_pages, uint, 0600);
>  MODULE_PARM_DESC(oom_pages, "pages to free on OOM");
>  
>  #ifdef CONFIG_BALLOON_COMPACTION
> @@ -359,16 +359,20 @@ static int virtballoon_oom_notify(struct notifier_block *self,
>  {
>  	struct virtio_balloon *vb;
>  	unsigned long *freed;
> -	unsigned num_freed_pages;
> +	unsigned int npages = oom_pages;
>  
>  	vb = container_of(self, struct virtio_balloon, nb);
>  	if (!virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
>  		return NOTIFY_OK;
>  
>  	freed = parm;
> -	num_freed_pages = leak_balloon(vb, oom_pages);
> +
> +	/* Don't deflate more than the number of inflated pages */
> +	while (npages && atomic64_read(&vb->num_pages))
> +		npages -= leak_balloon(vb, npages);
> +
>  	update_balloon_size(vb);
> -	*freed += num_freed_pages;
> +	*freed += oom_pages - npages;
>  
>  	return NOTIFY_OK;
>  }
> -- 
> 2.7.4