[PATCH R4 7/7] xen/balloon: Memory hotplug support for Xen balloon driver

[PATCH R4 7/7] xen/balloon: Memory hotplug support for Xen balloon driver

[Daniel Kiper]

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.

Signed-off-by: Daniel Kiper <dkiper@net-space.pl>
---
 drivers/xen/Kconfig   |   10 +++
 drivers/xen/balloon.c |  154 +++++++++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 159 insertions(+), 5 deletions(-)

diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
index 07bec09..8f880aa 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 431e9f0..3dc8a83 100644
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -6,6 +6,12 @@
  * 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
@@ -44,6 +50,9 @@
 #include <linux/list.h>
 #include <linux/sysdev.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>
@@ -93,6 +102,10 @@ 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
 };
 
 static DEFINE_MUTEX(balloon_mutex);
@@ -221,7 +234,93 @@ static enum bp_state update_schedule(enum bp_state state)
 	return BP_EAGAIN;
 }
 
-static unsigned long current_target(void)
+#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 int balloon_is_inflated(void)
+{
+	if (balloon_stats.balloon_low || balloon_stats.balloon_high ||
+			balloon_stats.balloon_hotplug)
+		return 1;
+	else
+		return 0;
+}
+
+static enum bp_state reserve_additional_memory(long credit)
+{
+	int rc;
+	unsigned long balloon_hotplug = credit;
+
+	balloon_hotplug <<= PAGE_SHIFT;
+
+	rc = add_virtual_memory((u64 *)&balloon_hotplug);
+
+	if (rc) {
+		pr_info("xen_balloon: %s: add_virtual_memory() failed: %i\n", __func__, rc);
+		return BP_EAGAIN;
+	}
+
+	balloon_hotplug >>= PAGE_SHIFT;
+
+	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;
+	unsigned long pfn = page_to_pfn(page);
+
+	if (pfn >= num_physpages)
+		num_physpages = pfn + 1;
+
+	inc_totalhigh_pages();
+
+#ifdef CONFIG_FLATMEM
+	max_mapnr = max(pfn, max_mapnr);
+#endif
+
+	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;
 
@@ -230,9 +329,24 @@ static unsigned long current_target(void)
 		     balloon_stats.balloon_low +
 		     balloon_stats.balloon_high);
 
-	return target;
+	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;
@@ -244,6 +358,15 @@ 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);
 
@@ -308,6 +431,15 @@ static enum bp_state decrease_reservation(unsigned long nr_pages)
 		.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);
 
@@ -368,10 +500,14 @@ static void balloon_process(struct work_struct *work)
 	mutex_lock(&balloon_mutex);
 
 	do {
-		credit = current_target() - balloon_stats.current_pages;
+		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);
@@ -458,6 +594,14 @@ static int __init balloon_init(void)
 	balloon_stats.retry_count = 1;
 	balloon_stats.max_retry_count = 16;
 
+#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
+
 	register_balloon(&balloon_sysdev);
 
 	/*
-- 
1.5.6.5

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Re: [PATCH R4 7/7] xen/balloon: Memory hotplug support for Xen balloon driver

[Dave Hansen]

On Tue, 2011-03-08 at 22:50 +0100, Daniel Kiper wrote:
> +static enum bp_state reserve_additional_memory(long credit)
> +{
> +	int rc;
> +	unsigned long balloon_hotplug = credit;
> +
> +	balloon_hotplug <<= PAGE_SHIFT;
> +
> +	rc = add_virtual_memory((u64 *)&balloon_hotplug);

This would work if all 'unsigned long's were 64-bits.  It'll break on
32-bit kernels in a very bad way by overwriting 4 bytes of stack.

> +	if (rc) {
> +		pr_info("xen_balloon: %s: add_virtual_memory() failed: %i\n", __func__, rc);
> +		return BP_EAGAIN;
> +	}
> +
> +	balloon_hotplug >>= PAGE_SHIFT;
> +
> +	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;
> +	unsigned long pfn = page_to_pfn(page);
> +
> +	if (pfn >= num_physpages)
> +		num_physpages = pfn + 1;
> +
> +	inc_totalhigh_pages();
> +
> +#ifdef CONFIG_FLATMEM
> +	max_mapnr = max(pfn, max_mapnr);
> +#endif

I really don't like that this is a direct copy of online_page() up to
this point.  They're already subtly different.  I'm also curious if this
breaks on 32-bit kernels because of the unconditional
inc_totalhigh_pages().

If it's done this way, I'd almost guarantee that the first time someone
fixes a bug or adds a generic feature in online_page() that Xen gets
missed.  

> +	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;
> +}

I'm not a _huge_ fan of these notifier chains, but I guess it works.
However, if you're going to use these notifier chains, then we probably
should use them to full effect.  Have a notifier list like this:

	1. generic online_page()
	2. xen_online_page_notifier() (returns NOTIFY_STOP)
	3. free_online_page()

Where finish_online_page() does something like this:

finish_online_page(...)
{
        ClearPageReserved(page);
        init_page_count(page);
        __free_page(page);
}

These patches are definitely getting there.  Just another round or two,
and they should be ready to go.

-- Dave

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Re: [Xen-devel] [PATCH R4 7/7] xen/balloon: Memory hotplug support for Xen balloon driver

[Konrad Rzeszutek Wilk]

> -		credit = current_target() - balloon_stats.current_pages;
> +		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);
> +		}

This code manipulation of where the current_target becomes current_credit
(and that logic) should be split off in its own patch.

Otherwise all the patches that touch Xen code look good.
>  
>  		if (credit < 0)
>  			state = decrease_reservation(-credit);
> @@ -458,6 +594,14 @@ static int __init balloon_init(void)
>  	balloon_stats.retry_count = 1;
>  	balloon_stats.max_retry_count = 16;
>  
> +#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
> +
>  	register_balloon(&balloon_sysdev);
>  
>  	/*
> -- 
> 1.5.6.5
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel

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Re: [PATCH R4 7/7] xen/balloon: Memory hotplug support for Xen balloon driver

[Daniel Kiper]

On Tue, Mar 08, 2011 at 04:02:19PM -0800, Dave Hansen wrote:
> On Tue, 2011-03-08 at 22:50 +0100, Daniel Kiper wrote:
> > +static int xen_online_page_notifier(struct notifier_block *nb, unsigned long val, void *v)
> > +{
> > +	struct page *page = v;
> > +	unsigned long pfn = page_to_pfn(page);
> > +
> > +	if (pfn >= num_physpages)
> > +		num_physpages = pfn + 1;
> > +
> > +	inc_totalhigh_pages();
> > +
> > +#ifdef CONFIG_FLATMEM
> > +	max_mapnr = max(pfn, max_mapnr);
> > +#endif
>
> I really don't like that this is a direct copy of online_page() up to
> this point.  They're already subtly different.  I'm also curious if this
> breaks on 32-bit kernels because of the unconditional
> inc_totalhigh_pages().
>
> If it's done this way, I'd almost guarantee that the first time someone
> fixes a bug or adds a generic feature in online_page() that Xen gets
> missed.

OK, I rewrite this part of code.

> > +	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;
> > +}
>
> I'm not a _huge_ fan of these notifier chains, but I guess it works.

Could you tell me why ??? I think that in that case new
(faster, simpler, etc.) mechanism is an overkill. I prefer
to use something which is writen, tested and ready for usage.

> However, if you're going to use these notifier chains, then we probably
> should use them to full effect.  Have a notifier list like this:
>
> 	1. generic online_page()
> 	2. xen_online_page_notifier() (returns NOTIFY_STOP)
> 	3. free_online_page()
>
> Where finish_online_page() does something like this:
>
> finish_online_page(...)
> {
>         ClearPageReserved(page);
>         init_page_count(page);
>         __free_page(page);
> }

OK.

Daniel

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Re: [PATCH R4 7/7] xen/balloon: Memory hotplug support for Xen balloon driver

[Dave Hansen]

On Thu, 2011-03-10 at 10:02 +0100, Daniel Kiper wrote:
> On Tue, Mar 08, 2011 at 04:02:19PM -0800, Dave Hansen wrote:
> > > +	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;
> > > +}
> >
> > I'm not a _huge_ fan of these notifier chains, but I guess it works.
> 
> Could you tell me why ??? I think that in that case new
> (faster, simpler, etc.) mechanism is an overkill. I prefer
> to use something which is writen, tested and ready for usage.

Personally, I find it much harder to figure out what's going on there
than if we had some #ifdefs or plain old function calls.  

It would be one thing if we really had a large or undefined set of
things that needs to interact here, but we really just need to
conditionally free the page either in to the buddy allocator or back to
Xen.  I think that calls for a simpler mechanism than notifier_blocks.

-- Dave

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