Re: [Qemu-devel] [PATCH RFC kernel] balloon: speed up inflating/deflating process

[Li, Liang Z]

> > > Interesting. How about instead of tell host, we do multiple scans,
> > > each time ignoring pages out of range?
> > >
> > >   for (pfn = min pfn; pfn < max pfn; pfn += 1G) {
> > >           foreach page
> > >                   if page pfn < pfn || page pfn >= pfn + 1G
> > >                           continue
> > >                   set bit
> > >           tell host
> > >   }
> > >
> >
> > That means we have to allocate/free all the requested pages first, and then
> tell the host.
> > It works fine for inflating, but for deflating, because the page has
> > been deleted from the vb-> vb_dev_info->pages, so, we have to use a
> > struct to save the dequeued pages before calling
> > release_pages_balloon(),
> 
> struct list_head?  I think you can just replace set_page_pfns with
>         list_add(&page->lru, &page_list);
> 
> 

That's is fine, I will retry and get back to you.

Thanks!

Liang
> 
> >  I think a page bitmap is the best struct to save these pages, because it
> consumes less memory.
> > And that bitmap should be large enough to save pfn 0 to max_pfn.
> >
> > If the above is true, then we are back to the square one. we really need a
> large page bitmap. Right?
> >
> > Liang
> 
> These look like implementation issues to me.
> 
> I think the below might be helpful (completely untested), your work can go
> on top.
> 
> --->
> 
> virtio-balloon: rework deflate to add page to a tmp list
> 
> Will allow faster notifications using a bitmap down the road.
> 
> Signed-off-by: Michael S. Tsirkin <address@hidden>
> 
> ---
> 
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 476c0e3..44050a3 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -195,8 +195,9 @@ static void release_pages_balloon(struct
> virtio_balloon *vb)  static unsigned leak_balloon(struct virtio_balloon *vb,
> size_t num)  {
>       unsigned num_freed_pages;
> -     struct page *page;
> +     struct page *page, *next;
>       struct balloon_dev_info *vb_dev_info = &vb->vb_dev_info;
> +     LIST_HEAD(pages);               /* Pages dequeued for handing to
> Host */
> 
>       /* We can only do one array worth at a time. */
>       num = min(num, ARRAY_SIZE(vb->pfns));
> @@ -207,10 +208,13 @@ static unsigned leak_balloon(struct virtio_balloon
> *vb, size_t num)
>               page = balloon_page_dequeue(vb_dev_info);
>               if (!page)
>                       break;
> -             set_page_pfns(vb, vb->pfns + vb->num_pfns, page);
> +             list_add(&page->lru, &pages);
>               vb->num_pages -= VIRTIO_BALLOON_PAGES_PER_PAGE;
>       }
> 
> +     list_for_each_entry_safe(page, next, &pages, lru)
> +             set_page_pfns(vb, vb->pfns + vb->num_pfns, page);
> +
>       num_freed_pages = vb->num_pfns;
>       /*
>        * Note that if
> --
> MST