linux-kernel - [RFC PATCH 4/4] virtio_balloon: skip inflation if guest is under pressure

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Date:	Thu, 16 Jan 2014 11:24:05 -0500
From:	Luiz Capitulino <lcapitulino@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	kvm@...r.kernel.org, riel@...hat.com, aarcange@...hat.com,
	aquini@...hat.com, mst@...hat.com, rusty@...tcorp.com.au,
	vdavydov@...allels.com, amit.shah@...hat.com, dfediuck@...hat.com,
	agl@...ibm.com
Subject: [RFC PATCH 4/4] virtio_balloon: skip inflation if guest is under pressure

From: Luiz capitulino <lcapitulino@...hat.com>

This is necessary for automatic ballooning. If the guest gets
under pressure while there's an on-going inflation operation,
we want the guest to do the following:

 1. Stop on-going inflation
 2. Notify the host we're under pressure
 3. Wait for host's acknowledge

While the guest is waiting the host has the opportunity to
reset num_pages to a value before the guest got into pressure.
This will cancel current inflation.

Signed-off-by: Luiz capitulino <lcapitulino@...hat.com>
---
 drivers/virtio/virtio_balloon.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 1c3ee71..7f5b7d2 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -188,8 +188,13 @@ static void fill_balloon(struct virtio_balloon *vb, size_t num)
 	mutex_lock(&vb->balloon_lock);
 	for (vb->num_pfns = 0; vb->num_pfns < num;
 	     vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
-		struct page *page = balloon_page_enqueue(vb_dev_info);
+	     	struct page *page;
 
+	     	if (guest_under_pressure(vb)) {
+			break;
+		}
+
+		page = balloon_page_enqueue(vb_dev_info);
 		if (!page) {
 			dev_info_ratelimited(&vb->vdev->dev,
 					     "Out of puff! Can't get %u pages\n",
-- 
1.8.1.4

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