linux-kernel - RE: [PATCH RFC kernel] balloon: speed up inflating/deflating process

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Date:	Wed, 25 May 2016 14:29:35 +0000
From:	"Li, Liang Z" <liang.z.li@...el.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"qemu-devel@...gnu.org" <qemu-devel@...gnu.org>,
	"virtualization@...ts.linux-foundation.org" 
	<virtualization@...ts.linux-foundation.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"pbonzini@...hat.com" <pbonzini@...hat.com>,
	"dgilbert@...hat.com" <dgilbert@...hat.com>,
	"amit.shah@...hat.com" <amit.shah@...hat.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: RE: [PATCH RFC kernel] balloon: speed up inflating/deflating process

> > > 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 <mst@...hat.com>
> 
> ---
> 
> 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