linux-kernel - Re: [PATCH 2/2] virtio_balloon: fix shrinker

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Date:   Mon, 18 Nov 2019 17:56:24 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Khazhismel Kumykov <khazhy@...gle.com>
Cc:     jasowang@...hat.com, wei.w.wang@...el.com,
        linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH 2/2] virtio_balloon: fix shrinker_scan return units

On Mon, Nov 18, 2019 at 01:38:11PM -0800, Khazhismel Kumykov wrote:
> We were returning number of virtio balloon pages, which may not be the
> same as number of system pages
> 
> Fixes: 86a559787e6f ("virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT")
> Cc: Wei Wang <wei.w.wang@...el.com>
> Signed-off-by: Khazhismel Kumykov <khazhy@...gle.com>
> ---
>  drivers/virtio/virtio_balloon.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 7cf9540a40b8..7951ece3fe24 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -802,11 +802,11 @@ static unsigned long virtio_balloon_shrinker_scan(struct shrinker *shrinker,
>  		pages_freed = shrink_free_pages(vb, pages_to_free);
>  
>  	if (pages_freed >= pages_to_free)
> -		return pages_freed;
> +		return pages_freed / VIRTIO_BALLOON_PAGES_PER_PAGE;
>

I'm no seeing why is this one right. shrink_free_pages gives result
in PAGE_SIZE units, right?
  
>  	pages_freed += shrink_balloon_pages(vb, pages_to_free - pages_freed);
>  
> -	return pages_freed;
> +	return pages_freed / VIRTIO_BALLOON_PAGES_PER_PAGE;


My head hurts. Isn't this what patch 1 tweaked?



>  }
>  
>  static unsigned long virtio_balloon_shrinker_count(struct shrinker *shrinker,
> -- 
> 2.24.0.432.g9d3f5f5b63-goog