Re: [Qemu-devel] [PATCH v16 3/5] virtio-balloon: VIRTIO_BALLOON_F_SG

[Michael S. Tsirkin]

On Sat, Sep 30, 2017 at 12:05:52PM +0800, Wei Wang wrote:
> +static inline void xb_set_page(struct virtio_balloon *vb,
> +                            struct page *page,
> +                            unsigned long *pfn_min,
> +                            unsigned long *pfn_max)
> +{
> +     unsigned long pfn = page_to_pfn(page);
> +
> +     *pfn_min = min(pfn, *pfn_min);
> +     *pfn_max = max(pfn, *pfn_max);
> +     xb_preload(GFP_KERNEL);
> +     xb_set_bit(&vb->page_xb, pfn);
> +     xb_preload_end();
> +}
> +

So, this will allocate memory

...

> @@ -198,9 +327,12 @@ static unsigned leak_balloon(struct virtio_balloon *vb, 
> size_t num)
>       struct page *page;
>       struct balloon_dev_info *vb_dev_info = &vb->vb_dev_info;
>       LIST_HEAD(pages);
> +     bool use_sg = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_SG);
> +     unsigned long pfn_max = 0, pfn_min = ULONG_MAX;
>  
> -     /* We can only do one array worth at a time. */
> -     num = min(num, ARRAY_SIZE(vb->pfns));
> +     /* Traditionally, we can only do one array worth at a time. */
> +     if (!use_sg)
> +             num = min(num, ARRAY_SIZE(vb->pfns));
>  
>       mutex_lock(&vb->balloon_lock);
>       /* We can't release more pages than taken */

And is sometimes called on OOM.


I suspect we need to

1. keep around some memory for leak on oom

2. for non oom allocate outside locks


-- 
MST