linux-kernel - [PATCHv2 06/10] xen/balloon: only hotplug additional memory if required

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Message-ID: <1437738468-24110-7-git-send-email-david.vrabel@citrix.com>
Date:	Fri, 24 Jul 2015 12:47:44 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	<xen-devel@...ts.xenproject.org>
CC:	David Vrabel <david.vrabel@...rix.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
	Daniel Kiper <daniel.kiper@...cle.com>
Subject: [PATCHv2 06/10] xen/balloon: only hotplug additional memory if required

Now that we track the total number of pages (included hotplugged
regions), it is easy to determine if more memory needs to be
hotplugged.

Add a new BP_WAIT state to signal that the balloon process needs to
wait until kicked by the memory add notifier (when the new section is
onlined by userspace).

Signed-off-by: David Vrabel <david.vrabel@...rix.com>
---
v2:
- New BP_WAIT status after adding new memory sections.
---
 drivers/xen/balloon.c | 23 +++++++++++++++++++----
 1 file changed, 19 insertions(+), 4 deletions(-)

diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index b5037b1..ced34cd 100644
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -75,12 +75,14 @@
  * balloon_process() state:
  *
  * BP_DONE: done or nothing to do,
+ * BP_WAIT: wait to be rescheduled,
  * BP_EAGAIN: error, go to sleep,
  * BP_ECANCELED: error, balloon operation canceled.
  */
 
 enum bp_state {
 	BP_DONE,
+	BP_WAIT,
 	BP_EAGAIN,
 	BP_ECANCELED
 };
@@ -167,6 +169,9 @@ static struct page *balloon_next_page(struct page *page)
 
 static enum bp_state update_schedule(enum bp_state state)
 {
+	if (state == BP_WAIT)
+		return BP_WAIT;
+
 	if (state == BP_ECANCELED)
 		return BP_ECANCELED;
 
@@ -242,12 +247,22 @@ static void release_memory_resource(struct resource *resource)
  * bit set). Real size of added memory is established at page onlining stage.
  */
 
-static enum bp_state reserve_additional_memory(long credit)
+static enum bp_state reserve_additional_memory(void)
 {
+	long credit;
 	struct resource *resource;
 	int nid, rc;
 	unsigned long balloon_hotplug;
 
+	credit = balloon_stats.target_pages - balloon_stats.total_pages;
+
+	/*
+	 * Already hotplugged enough pages?  Wait for them to be
+	 * onlined.
+	 */
+	if (credit <= 0)
+		return BP_EAGAIN;
+
 	balloon_hotplug = round_up(credit, PAGES_PER_SECTION);
 
 	resource = additional_memory_resource(balloon_hotplug * PAGE_SIZE);
@@ -287,7 +302,7 @@ static enum bp_state reserve_additional_memory(long credit)
 
 	balloon_stats.total_pages += balloon_hotplug;
 
-	return BP_DONE;
+	return BP_WAIT;
   err:
 	release_memory_resource(resource);
 	return BP_ECANCELED;
@@ -317,7 +332,7 @@ static struct notifier_block xen_memory_nb = {
 	.priority = 0
 };
 #else
-static enum bp_state reserve_additional_memory(long credit)
+static enum bp_state reserve_additional_memory(void)
 {
 	balloon_stats.target_pages = balloon_stats.current_pages;
 	return BP_DONE;
@@ -484,7 +499,7 @@ static void balloon_process(struct work_struct *work)
 			if (balloon_is_inflated())
 				state = increase_reservation(credit);
 			else
-				state = reserve_additional_memory(credit);
+				state = reserve_additional_memory();
 		}
 
 		if (credit < 0)
-- 
2.1.4

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