[PATCH] xen/balloon: Memory hotplug support for Xen balloon driver

[Daniel Kiper <dkiper@net-space.pl>]

Memory hotplug support for Xen balloon driver. It should be
mentioned that hotplugged memory is not onlined automatically.
It should be onlined by user through standard sysfs interface.

There are a few prerequisite patches which fixes some problems
found during work on memory hotplug patch or add some futures
which are needed by this patch. They are available here:
  - https://lkml.org/lkml/2011/3/28/94,
  - https://lkml.org/lkml/2011/3/28/98.

I have received notice that previous series of patches broke
machine migration under Xen. I am going to confirm that and
solve that problem ASAP. I do not have received any notices
about other problems till now.

Signed-off-by: Daniel Kiper <dkiper@net-space.pl>
---
 drivers/xen/Kconfig   |   10 +++
 drivers/xen/balloon.c |  148 ++++++++++++++++++++++++++++++++++++++++++++++++-
 include/xen/balloon.h |    4 +
 3 files changed, 160 insertions(+), 2 deletions(-)

diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
index e5ecae6..39df71b 100644
--- a/drivers/xen/Kconfig
+++ b/drivers/xen/Kconfig
@@ -9,6 +9,16 @@ config XEN_BALLOON
 	  the system to expand the domain's memory allocation, or alternatively
 	  return unneeded memory to the system.
 
+config XEN_BALLOON_MEMORY_HOTPLUG
+	bool "Memory hotplug support for Xen balloon driver"
+	default n
+	depends on XEN_BALLOON && MEMORY_HOTPLUG
+	help
+	  Memory hotplug support for Xen balloon driver allows expanding memory
+	  available for the system above limit declared at system startup.
+	  It is very useful on critical systems which require long
+	  run without rebooting.
+
 config XEN_SCRUB_PAGES
 	bool "Scrub pages before returning them to system"
 	depends on XEN_BALLOON
diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index f54290b..189023e 100644
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -4,6 +4,12 @@
  * Copyright (c) 2003, B Dragovic
  * Copyright (c) 2003-2004, M Williamson, K Fraser
  * Copyright (c) 2005 Dan M. Smith, IBM Corporation
+ * Copyright (c) 2010 Daniel Kiper
+ *
+ * Memory hotplug support was written by Daniel Kiper. Work on
+ * it was sponsored by Google under Google Summer of Code 2010
+ * program. Jeremy Fitzhardinge from Xen.org was the mentor for
+ * this project.
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License version 2
@@ -40,6 +46,9 @@
 #include <linux/mutex.h>
 #include <linux/list.h>
 #include <linux/gfp.h>
+#include <linux/notifier.h>
+#include <linux/memory.h>
+#include <linux/memory_hotplug.h>
 
 #include <asm/page.h>
 #include <asm/pgalloc.h>
@@ -194,6 +203,96 @@ static enum bp_state update_schedule(enum bp_state state)
 	return BP_EAGAIN;
 }
 
+#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
+static long current_credit(void)
+{
+	return balloon_stats.target_pages - balloon_stats.current_pages -
+		balloon_stats.hotplug_pages;
+}
+
+static bool balloon_is_inflated(void)
+{
+	if (balloon_stats.balloon_low || balloon_stats.balloon_high ||
+			balloon_stats.balloon_hotplug)
+		return true;
+	else
+		return false;
+}
+
+/*
+ * reserve_additional_memory() adds memory region of size >= credit above
+ * max_pfn. New region is section aligned and size is modified to be multiple
+ * of section size. Those features allow optimal use of address space and
+ * establish proper alignment when this function is called first time after
+ * boot (last section not fully populated at boot time may contains unused
+ * memory pages with PG_reserved bit not set; online_pages() does not allow
+ * page onlining in whole section if first page does not have PG_reserved
+ * bit set). Real size of added memory is established at page onlining stage.
+ */
+
+static enum bp_state reserve_additional_memory(long credit)
+{
+	int nid, rc;
+	u64 start;
+	unsigned long balloon_hotplug = credit;
+
+	start = PFN_PHYS(SECTION_ALIGN_UP(max_pfn));
+	balloon_hotplug = (balloon_hotplug & PAGE_SECTION_MASK) + PAGES_PER_SECTION;
+	nid = memory_add_physaddr_to_nid(start);
+
+	rc = add_memory(nid, start, balloon_hotplug << PAGE_SHIFT);
+
+	if (rc) {
+		pr_info("xen_balloon: %s: add_memory() failed: %i\n", __func__, rc);
+		return BP_EAGAIN;
+	}
+
+	balloon_hotplug -= credit;
+
+	balloon_stats.hotplug_pages += credit;
+	balloon_stats.balloon_hotplug = balloon_hotplug;
+
+	return BP_DONE;
+}
+
+static int xen_online_page_notifier(struct notifier_block *nb, unsigned long val, void *v)
+{
+	struct page *page = v;
+
+	__online_page_increment_counters(page, OP_DO_NOT_INCREMENT_TOTAL_COUNTERS);
+
+	mutex_lock(&balloon_mutex);
+
+	__balloon_append(page);
+
+	if (balloon_stats.hotplug_pages)
+		--balloon_stats.hotplug_pages;
+	else
+		--balloon_stats.balloon_hotplug;
+
+	mutex_unlock(&balloon_mutex);
+
+	return NOTIFY_STOP;
+}
+
+static struct notifier_block xen_online_page_nb = {
+	.notifier_call = xen_online_page_notifier,
+	.priority = 10
+};
+
+static int xen_memory_notifier(struct notifier_block *nb, unsigned long val, void *v)
+{
+	if (val == MEM_ONLINE)
+		schedule_delayed_work(&balloon_worker, 0);
+
+	return NOTIFY_OK;
+}
+
+static struct notifier_block xen_memory_nb = {
+	.notifier_call = xen_memory_notifier,
+	.priority = 0
+};
+#else
 static long current_credit(void)
 {
 	unsigned long target = balloon_stats.target_pages;
@@ -206,6 +305,21 @@ static long current_credit(void)
 	return target - balloon_stats.current_pages;
 }
 
+static int balloon_is_inflated(void)
+{
+	if (balloon_stats.balloon_low || balloon_stats.balloon_high)
+		return 1;
+	else
+		return 0;
+}
+
+static enum bp_state reserve_additional_memory(long credit)
+{
+	balloon_stats.target_pages = balloon_stats.current_pages;
+	return BP_DONE;
+}
+#endif /* CONFIG_XEN_BALLOON_MEMORY_HOTPLUG */
+
 static enum bp_state increase_reservation(unsigned long nr_pages)
 {
 	int rc;
@@ -217,6 +331,15 @@ static enum bp_state increase_reservation(unsigned long nr_pages)
 		.domid        = DOMID_SELF
 	};
 
+#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
+	if (!balloon_stats.balloon_low && !balloon_stats.balloon_high) {
+		nr_pages = min(nr_pages, balloon_stats.balloon_hotplug);
+		balloon_stats.hotplug_pages += nr_pages;
+		balloon_stats.balloon_hotplug -= nr_pages;
+		return BP_DONE;
+	}
+#endif
+
 	if (nr_pages > ARRAY_SIZE(frame_list))
 		nr_pages = ARRAY_SIZE(frame_list);
 
@@ -279,6 +402,15 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
 		.domid        = DOMID_SELF
 	};
 
+#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
+	if (balloon_stats.hotplug_pages) {
+		nr_pages = min(nr_pages, balloon_stats.hotplug_pages);
+		balloon_stats.hotplug_pages -= nr_pages;
+		balloon_stats.balloon_hotplug += nr_pages;
+		return BP_DONE;
+	}
+#endif
+
 	if (nr_pages > ARRAY_SIZE(frame_list))
 		nr_pages = ARRAY_SIZE(frame_list);
 
@@ -340,8 +472,12 @@ static void balloon_process(struct work_struct *work)
 	do {
 		credit = current_credit();
 
-		if (credit > 0)
-			state = increase_reservation(credit);
+		if (credit > 0) {
+			if (balloon_is_inflated())
+				state = increase_reservation(credit);
+			else
+				state = reserve_additional_memory(credit);
+		}
 
 		if (credit < 0)
 			state = decrease_reservation(-credit, GFP_BALLOON);
@@ -448,6 +584,14 @@ static int __init balloon_init(void)
 	balloon_stats.retry_count = 1;
 	balloon_stats.max_retry_count = RETRY_UNLIMITED;
 
+#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
+	balloon_stats.hotplug_pages = 0;
+	balloon_stats.balloon_hotplug = 0;
+
+	register_online_page_notifier(&xen_online_page_nb);
+	register_memory_notifier(&xen_memory_nb);
+#endif
+
 	/*
 	 * Initialise the balloon with excess memory space.  We need
 	 * to make sure we don't add memory which doesn't exist or
diff --git a/include/xen/balloon.h b/include/xen/balloon.h
index a2b22f0..aeca6ae 100644
--- a/include/xen/balloon.h
+++ b/include/xen/balloon.h
@@ -15,6 +15,10 @@ struct balloon_stats {
 	unsigned long max_schedule_delay;
 	unsigned long retry_count;
 	unsigned long max_retry_count;
+#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
+	unsigned long hotplug_pages;
+	unsigned long balloon_hotplug;
+#endif
 };
 
 extern struct balloon_stats balloon_stats;
-- 
1.5.6.5

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