[PATCH 2/2] Drivers: hv: hv_balloon: refuse to balloon below the floor

[Vitaly Kuznetsov <vkuznets@redhat.com>]

When host asks us to balloon up we need to be sure we're not committing suicide
by overballooning. Use already existent 'floor' metric as our lowest possible
value for free ram.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
 drivers/hv/hv_balloon.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
index e4b4454..3292e97 100644
--- a/drivers/hv/hv_balloon.c
+++ b/drivers/hv/hv_balloon.c
@@ -1138,6 +1138,8 @@ static void balloon_up(struct work_struct *dummy)
 	bool alloc_error;
 	bool done = false;
 	int i;
+	struct sysinfo val;
+	unsigned long floor;
 
 	/* The host balloons pages in 2M granularity. */
 	WARN_ON_ONCE(num_pages % PAGES_IN_2M != 0);
@@ -1148,6 +1150,15 @@ static void balloon_up(struct work_struct *dummy)
 	 */
 	alloc_unit = 512;
 
+	si_meminfo(&val);
+	floor = compute_balloon_floor();
+
+	/* Refuse to balloon below the floor, keep the 2M granularity. */
+	if (val.freeram - num_pages < floor) {
+		num_pages = val.freeram > floor ? (val.freeram - floor) : 0;
+		num_pages -= num_pages % PAGES_IN_2M;
+	}
+
 	while (!done) {
 		bl_resp = (struct dm_balloon_response *)send_buffer;
 		memset(send_buffer, 0, PAGE_SIZE);
-- 
1.9.3