RE: [PATCH v2 repost 7/7] virtio-balloon: tell host vm's free page info

Li, Liang Z
2016-07-28T07:50:52Z

> > }
> >
> > +static void update_free_pages_stats(struct virtio_balloon *vb,
>
> why _stats?

Will change.

> > + max_pfn = get_max_pfn();
> > + mutex_lock(&vb->balloon_lock);
> > + while (pfn < max_pfn) {
> > + memset(vb->page_bitmap, 0, vb->bmap_len);
> > + ret = get_free_pages(pfn, pfn + vb->pfn_limit,
> > + vb->page_bitmap, vb->bmap_len * BITS_PER_BYTE);
> > + hdr->cmd = cpu_to_virtio16(vb->vdev,
> BALLOON_GET_FREE_PAGES);
> > + hdr->page_shift = cpu_to_virtio16(vb->vdev, PAGE_SHIFT);
> > + hdr->req_id = cpu_to_virtio64(vb->vdev, req_id);
> > + hdr->start_pfn = cpu_to_virtio64(vb->vdev, pfn);
> > + bmap_len = vb->pfn_limit / BITS_PER_BYTE;
> > + if (!ret) {
> > + hdr->flag = cpu_to_virtio16(vb->vdev,
> > +
> BALLOON_FLAG_DONE);
> > + if (pfn + vb->pfn_limit > max_pfn)
> > + bmap_len = (max_pfn - pfn) /
> BITS_PER_BYTE;
> > + } else
> > + hdr->flag = cpu_to_virtio16(vb->vdev,
> > +
> BALLOON_FLAG_CONT);
> > + hdr->bmap_len = cpu_to_virtio64(vb->vdev, bmap_len);
> > + sg_init_one(&sg_out, hdr,
> > + sizeof(struct balloon_bmap_hdr) + bmap_len);
>
> Wait a second. This adds the same buffer multiple times in a loop.
> We will overwrite the buffer without waiting for hypervisor to process it.
> What did I miss?

I am no quite sure about this part, I though the virtqueue_kick(vq) will prevent
the buffer from overwrite, I realized it's wrong.

> > +
> > + virtqueue_add_outbuf(vq, &sg_out, 1, vb, GFP_KERNEL);
>
> this can fail. you want to maybe make sure vq has enough space before you
> use it or check error and wait.
>
> > + virtqueue_kick(vq);
>
> why kick here within loop? wait until done. in fact kick outside lock is better
> for smp.

I will change this part in v3.

>
> > + pfn += vb->pfn_limit;
> > + static const char * const names[] = { "inflate", "deflate", "stats",
> > + "misc" };
> > int err, nvqs;
> >
> > /*
> > * We expect two virtqueues: inflate and deflate, and
> > * optionally stat.
> > */
> > - nvqs = virtio_has_feature(vb->vdev,
> VIRTIO_BALLOON_F_STATS_VQ) ? 3 : 2;
> > + if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_MISC_VQ))
> > + nvqs = 4;
>
> Does misc vq depend on stats vq feature then? if yes please validate that.

Yes, what's you mean by 'validate' that?

>
>
> > + else
> > + nvqs = virtio_has_feature(vb->vdev,
> > + VIRTIO_BALLOON_F_STATS_VQ) ? 3 :
> 2;
>
> Replace that ? with else too pls.

Will change.

Thanks!
Liang