Re: [Qemu-devel] [RESEND PATCH v3 kernel 1/7] virtio-balloon: rework deflate to add page to a list

[Li, Liang Z]

> On 10/20/2016 11:24 PM, Liang Li wrote:
> > Will allow faster notifications using a bitmap down the road.
> > balloon_pfn_to_page() can be removed because it's useless.
> 
> This is a pretty terse description of what's going on here.  Could you try to
> elaborate a bit?  What *is* the current approach?  Why does it not work
> going forward?  What do you propose instead?  Why is it better?

Sure. The description will be more clear if it's described as you suggest. 
Thanks!

Liang 

Re: [Qemu-devel] [RESEND PATCH v3 kernel 1/7] virtio-balloon: rework deflate to add page to a list

[Dave Hansen]

On 10/20/2016 11:24 PM, Liang Li wrote:
> Will allow faster notifications using a bitmap down the road.
> balloon_pfn_to_page() can be removed because it's useless.

This is a pretty terse description of what's going on here.  Could you
try to elaborate a bit?  What *is* the current approach?  Why does it
not work going forward?  What do you propose instead?  Why is it better?

[Qemu-devel] [RESEND PATCH v3 kernel 1/7] virtio-balloon: rework deflate to add page to a list

[Liang Li]

Will allow faster notifications using a bitmap down the road.
balloon_pfn_to_page() can be removed because it's useless.

Signed-off-by: Liang Li 
Signed-off-by: Michael S. Tsirkin 
Cc: Paolo Bonzini 
Cc: Cornelia Huck 
Cc: Amit Shah 
---
 drivers/virtio/virtio_balloon.c | 22 --
 1 file changed, 8 insertions(+), 14 deletions(-)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 4e7003d..59ffe5a 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -103,12 +103,6 @@ static u32 page_to_balloon_pfn(struct page *page)
return pfn * VIRTIO_BALLOON_PAGES_PER_PAGE;
 }
 
-static struct page *balloon_pfn_to_page(u32 pfn)
-{
-   BUG_ON(pfn % VIRTIO_BALLOON_PAGES_PER_PAGE);
-   return pfn_to_page(pfn / VIRTIO_BALLOON_PAGES_PER_PAGE);
-}
-
 static void balloon_ack(struct virtqueue *vq)
 {
struct virtio_balloon *vb = vq->vdev->priv;
@@ -181,18 +175,16 @@ static unsigned fill_balloon(struct virtio_balloon *vb, 
size_t num)
return num_allocated_pages;
 }
 
-static void release_pages_balloon(struct virtio_balloon *vb)
+static void release_pages_balloon(struct virtio_balloon *vb,
+struct list_head *pages)
 {
-   unsigned int i;
-   struct page *page;
+   struct page *page, *next;
 
-   /* Find pfns pointing at start of each page, get pages and free them. */
-   for (i = 0; i < vb->num_pfns; i += VIRTIO_BALLOON_PAGES_PER_PAGE) {
-   page = balloon_pfn_to_page(virtio32_to_cpu(vb->vdev,
-  vb->pfns[i]));
+   list_for_each_entry_safe(page, next, pages, lru) {
if (!virtio_has_feature(vb->vdev,
VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
adjust_managed_page_count(page, 1);
+   list_del(>lru);
put_page(page); /* balloon reference */
}
 }
@@ -202,6 +194,7 @@ static unsigned leak_balloon(struct virtio_balloon *vb, 
size_t num)
unsigned num_freed_pages;
struct page *page;
struct balloon_dev_info *vb_dev_info = >vb_dev_info;
+   LIST_HEAD(pages);
 
/* We can only do one array worth at a time. */
num = min(num, ARRAY_SIZE(vb->pfns));
@@ -215,6 +208,7 @@ static unsigned leak_balloon(struct virtio_balloon *vb, 
size_t num)
if (!page)
break;
set_page_pfns(vb, vb->pfns + vb->num_pfns, page);
+   list_add(>lru, );
vb->num_pages -= VIRTIO_BALLOON_PAGES_PER_PAGE;
}
 
@@ -226,7 +220,7 @@ static unsigned leak_balloon(struct virtio_balloon *vb, 
size_t num)
 */
if (vb->num_pfns != 0)
tell_host(vb, vb->deflate_vq);
-   release_pages_balloon(vb);
+   release_pages_balloon(vb, );
mutex_unlock(>balloon_lock);
return num_freed_pages;
 }
-- 
1.8.3.1