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Subject[PATCH] GSoC 2010 - Memory hotplug support for Xen guests - patch for review only
Hello,

As I promised I am sending first patch which enables
memory hotplug in Xen guests. It is version for review
only. It has been tested on Xen Ver 4.0.0 in PV guest x86_64
with Linux kernel Ver. 2.6.32.16. In general it works,
however... For details look below...

This patch enables two modes of operation:
- enabled by CONFIG_XEN_MEMORY_HOTPLUG config option:
- set memory limit for chosen domU from dom0:
xm mem-max <domU> <new_memory_size_limit>
- add memory in chosen domU: echo <unused_address> > \
/sys/devices/system/memory/probe
- online memory in chosen domU: echo online > \
/sys/devices/system/memory/memory<section_number>/state
- enabled by CONFIG_XEN_BALLOON_MEMORY_HOTPLUG config option:
- set memory limit for chosen domU from dom0:
xm mem-max <domU> <new_memory_size_limit>
- add memory for chosen domU from dom0:
xm mem-set <domU> <new_memory_size>
TODO:
- there is bug which generate oops when memory
is added and removed a few times from domU
(CONFIG_XEN_BALLOON_MEMORY_HOTPLUG); probably
I missed something,
- there is no synchronization between CONFIG_XEN_MEMORY_HOTPLUG
and CONFIG_XEN_BALLOON_MEMORY_HOTPLUG yet; memory
added from domU is not added to balloon_stats,
- some additional error checking should be implemented,
- final patch will be available for Linux kernel
Ver. 2.6.32.y, latest stable and RC,
- tests on all planned platforms.

I am waiting for your comments.

Daniel

diff -Nru linux-2.6.32.16.orig/drivers/base/memory.c linux-2.6.32.16/drivers/base/memory.c
--- linux-2.6.32.16.orig/drivers/base/memory.c 2010-07-05 20:14:00.000000000 +0200
+++ linux-2.6.32.16/drivers/base/memory.c 2010-07-16 11:48:45.000000000 +0200
@@ -3,6 +3,7 @@
*
* Written by Matt Tolentino <matthew.e.tolentino@intel.com>
* Dave Hansen <haveblue@us.ibm.com>
+ * Daniel Kiper <dkiper@net-space.pl>
*
* This file provides the necessary infrastructure to represent
* a SPARSEMEM-memory-model system's physical memory in /sysfs.
@@ -26,6 +27,16 @@
#include <asm/atomic.h>
#include <asm/uaccess.h>

+#ifdef CONFIG_XEN_MEMORY_HOTPLUG
+#include <linux/vmalloc.h>
+#include <asm/xen/hypervisor.h>
+#include <asm/xen/hypercall.h>
+#include <xen/interface/xen.h>
+#include <xen/interface/memory.h>
+#include <xen/features.h>
+#include <xen/page.h>
+#endif
+
#define MEMORY_CLASS_NAME "memory"

static struct sysdev_class memory_sysdev_class = {
@@ -314,13 +325,61 @@
memory_probe_store(struct class *class, const char *buf, size_t count)
{
u64 phys_addr;
- int nid;
- int ret;
+ long ret;
+
+#ifdef CONFIG_XEN_MEMORY_HOTPLUG
+ struct xen_memory_reservation reservation = {
+ .address_bits = 0,
+ .extent_order = 0,
+ .domid = DOMID_SELF,
+ .nr_extents = PAGES_PER_SECTION
+ };
+ unsigned long *frame_list, i, nr_pages, pfn;
+#endif

phys_addr = simple_strtoull(buf, NULL, 0);

- nid = memory_add_physaddr_to_nid(phys_addr);
- ret = add_memory(nid, phys_addr, PAGES_PER_SECTION << PAGE_SHIFT);
+#ifdef CONFIG_XEN_MEMORY_HOTPLUG
+ if (xen_domain()) {
+ if (!(frame_list = vmalloc(PAGES_PER_SECTION * sizeof(unsigned long)))) {
+ printk(KERN_ERR "%s: vmalloc: Out of memory\n", __func__);
+ return -ENOMEM;
+ }
+
+ set_xen_guest_handle(reservation.extent_start, frame_list);
+ for (i = 0, pfn = phys_addr >> PAGE_SHIFT; i < PAGES_PER_SECTION; ++i, ++pfn)
+ frame_list[i] = pfn;
+
+ ret = HYPERVISOR_memory_op(XENMEM_populate_physmap, &reservation);
+
+ if (ret < PAGES_PER_SECTION) {
+ if (ret > 0) {
+ printk(KERN_ERR "%s: PHYSMAP is not fully populated: %li/%lu\n",
+ __func__, ret, PAGES_PER_SECTION);
+ reservation.nr_extents = nr_pages = ret;
+ ret = HYPERVISOR_memory_op(XENMEM_decrease_reservation, &reservation);
+ BUG_ON(ret != nr_pages);
+ ret = -ENOMEM;
+ } else {
+ ret = (ret < 0) ? ret : -ENOMEM;
+ printk(KERN_ERR "%s: Can't populate PHYSMAP: %li\n", __func__, ret);
+ }
+ vfree(frame_list);
+ return ret;
+ }
+
+ for (i = 0, pfn = phys_addr >> PAGE_SHIFT; i < PAGES_PER_SECTION; ++i, ++pfn) {
+ BUG_ON(!xen_feature(XENFEAT_auto_translated_physmap) &&
+ phys_to_machine_mapping_valid(pfn));
+ set_phys_to_machine(pfn, frame_list[i]);
+ }
+
+ vfree(frame_list);
+ }
+#endif
+
+ ret = add_memory(memory_add_physaddr_to_nid(phys_addr),
+ phys_addr, PAGES_PER_SECTION << PAGE_SHIFT);

if (ret)
count = ret;
diff -Nru linux-2.6.32.16.orig/drivers/xen/Kconfig linux-2.6.32.16/drivers/xen/Kconfig
--- linux-2.6.32.16.orig/drivers/xen/Kconfig 2010-07-05 20:14:00.000000000 +0200
+++ linux-2.6.32.16/drivers/xen/Kconfig 2010-07-09 21:04:17.000000000 +0200
@@ -7,6 +7,16 @@
the system to expand the domain's memory allocation, or alternatively
return unneeded memory to the system.

+config XEN_BALLOON_MEMORY_HOTPLUG
+ bool "Xen memory balloon driver with memory hotplug support"
+ depends on EXPERIMENTAL && XEN && XEN_BALLOON && MEMORY_HOTPLUG
+ default n
+ help
+ Xen memory balloon driver with memory hotplug support 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
@@ -60,4 +70,4 @@
Create entries under /sys/hypervisor describing the Xen
hypervisor environment. When running native or in another
virtual environment, /sys/hypervisor will still be present,
- but will have no xen contents.
\ No newline at end of file
+ but will have no xen contents.
diff -Nru linux-2.6.32.16.orig/drivers/xen/balloon.c linux-2.6.32.16/drivers/xen/balloon.c
--- linux-2.6.32.16.orig/drivers/xen/balloon.c 2010-07-05 20:14:00.000000000 +0200
+++ linux-2.6.32.16/drivers/xen/balloon.c 2010-07-16 15:06:53.000000000 +0200
@@ -6,6 +6,7 @@
* 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
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License version 2
@@ -74,6 +75,10 @@
/* Number of pages in high- and low-memory balloons. */
unsigned long balloon_low;
unsigned long balloon_high;
+#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
+ u64 hotplug_start_addr;
+ u64 hotplug_size;
+#endif
};

static DEFINE_MUTEX(balloon_mutex);
@@ -183,6 +188,9 @@

static unsigned long current_target(void)
{
+#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
+ return balloon_stats.target_pages;
+#else
unsigned long target = balloon_stats.target_pages;

target = min(target,
@@ -191,6 +199,7 @@
balloon_stats.balloon_high);

return target;
+#endif
}

static int increase_reservation(unsigned long nr_pages)
@@ -204,17 +213,48 @@
.domid = DOMID_SELF
};

+#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
+ struct resource *r;
+#endif
+
if (nr_pages > ARRAY_SIZE(frame_list))
nr_pages = ARRAY_SIZE(frame_list);

spin_lock_irqsave(&balloon_lock, flags);

+#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
+ if (!balloon_stats.balloon_low && !balloon_stats.balloon_high) {
+ if (!balloon_stats.hotplug_start_addr)
+ for (r = iomem_resource.child; r; r = r->sibling)
+ if (!r->sibling || r->sibling->start >
+ (((r->end >> PAGE_SHIFT) + balloon_stats.target_pages -
+ balloon_stats.current_pages) << PAGE_SHIFT)) {
+ balloon_stats.hotplug_start_addr = (((r->end >> PAGE_SHIFT) + 1) << PAGE_SHIFT);
+ break;
+ }
+
+ pfn = (balloon_stats.hotplug_start_addr + balloon_stats.hotplug_size) >> PAGE_SHIFT;
+
+ for (i = 0; i < nr_pages; ++i, ++pfn)
+ frame_list[i] = pfn;
+
+ pfn -= nr_pages + 1;
+ } else {
+ page = balloon_first_page();
+ for (i = 0; i < nr_pages; i++) {
+ BUG_ON(page == NULL);
+ frame_list[i] = page_to_pfn(page);
+ page = balloon_next_page(page);
+ }
+ }
+#else
page = balloon_first_page();
for (i = 0; i < nr_pages; i++) {
BUG_ON(page == NULL);
frame_list[i] = page_to_pfn(page);
page = balloon_next_page(page);
}
+#endif

set_xen_guest_handle(reservation.extent_start, frame_list);
reservation.nr_extents = nr_pages;
@@ -223,15 +263,30 @@
goto out;

for (i = 0; i < rc; i++) {
+#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
+ if (balloon_stats.hotplug_start_addr)
+ ++pfn;
+ else {
+ page = balloon_retrieve();
+ BUG_ON(page == NULL);
+ pfn = page_to_pfn(page);
+ }
+#else
page = balloon_retrieve();
BUG_ON(page == NULL);
-
pfn = page_to_pfn(page);
+#endif
+
BUG_ON(!xen_feature(XENFEAT_auto_translated_physmap) &&
phys_to_machine_mapping_valid(pfn));

set_phys_to_machine(pfn, frame_list[i]);

+#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
+ if (balloon_stats.hotplug_start_addr)
+ continue;
+#endif
+
/* Link back into the page tables if not highmem. */
if (pfn < max_low_pfn) {
int ret;
@@ -248,6 +303,11 @@
__free_page(page);
}

+#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
+ if (balloon_stats.hotplug_start_addr)
+ balloon_stats.hotplug_size += rc << PAGE_SHIFT;
+#endif
+
balloon_stats.current_pages += rc;

out:
@@ -344,8 +404,24 @@
} while ((credit != 0) && !need_sleep);

/* Schedule more work if there is some still to be done. */
+
+#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
if (current_target() != balloon_stats.current_pages)
mod_timer(&balloon_timer, jiffies + HZ);
+ else
+ if (balloon_stats.hotplug_start_addr) {
+ /* TODO: deallocate memory if something goes wrong !!! */
+ add_memory(memory_add_physaddr_to_nid(balloon_stats.hotplug_start_addr),
+ balloon_stats.hotplug_start_addr, balloon_stats.hotplug_size);
+ online_pages(balloon_stats.hotplug_start_addr >> PAGE_SHIFT,
+ balloon_stats.hotplug_size >> PAGE_SHIFT);
+ balloon_stats.hotplug_start_addr = 0;
+ balloon_stats.hotplug_size = 0;
+ }
+#else
+ if (current_target() != balloon_stats.current_pages)
+ mod_timer(&balloon_timer, jiffies + HZ);
+#endif

mutex_unlock(&balloon_mutex);
}
@@ -413,6 +489,11 @@
balloon_stats.balloon_high = 0;
balloon_stats.driver_pages = 0UL;

+#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
+ balloon_stats.hotplug_start_addr = 0;
+ balloon_stats.hotplug_size = 0;
+#endif
+
init_timer(&balloon_timer);
balloon_timer.data = 0;
balloon_timer.function = balloon_alarm;
diff -Nru linux-2.6.32.16.orig/mm/Kconfig linux-2.6.32.16/mm/Kconfig
--- linux-2.6.32.16.orig/mm/Kconfig 2010-07-05 20:14:00.000000000 +0200
+++ linux-2.6.32.16/mm/Kconfig 2010-07-16 11:44:27.000000000 +0200
@@ -140,6 +140,15 @@
depends on MEMORY_HOTPLUG && ARCH_ENABLE_MEMORY_HOTREMOVE
depends on MIGRATION

+config XEN_MEMORY_HOTPLUG
+ bool "Allow for memory hot-add in Xen guests"
+ depends on EXPERIMENTAL && ARCH_MEMORY_PROBE && XEN
+ default n
+ help
+ Memory hot-add 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.
+
#
# If we have space for more page flags then we can enable additional
# optimizations and functionality.diff -Nru linux-2.6.32.16.orig/drivers/base/memory.c linux-2.6.32.16/drivers/base/memory.c
--- linux-2.6.32.16.orig/drivers/base/memory.c 2010-07-05 20:14:00.000000000 +0200
+++ linux-2.6.32.16/drivers/base/memory.c 2010-07-16 11:48:45.000000000 +0200
@@ -3,6 +3,7 @@
*
* Written by Matt Tolentino <matthew.e.tolentino@intel.com>
* Dave Hansen <haveblue@us.ibm.com>
+ * Daniel Kiper <dkiper@net-space.pl>
*
* This file provides the necessary infrastructure to represent
* a SPARSEMEM-memory-model system's physical memory in /sysfs.
@@ -26,6 +27,16 @@
#include <asm/atomic.h>
#include <asm/uaccess.h>

+#ifdef CONFIG_XEN_MEMORY_HOTPLUG
+#include <linux/vmalloc.h>
+#include <asm/xen/hypervisor.h>
+#include <asm/xen/hypercall.h>
+#include <xen/interface/xen.h>
+#include <xen/interface/memory.h>
+#include <xen/features.h>
+#include <xen/page.h>
+#endif
+
#define MEMORY_CLASS_NAME "memory"

static struct sysdev_class memory_sysdev_class = {
@@ -314,13 +325,61 @@
memory_probe_store(struct class *class, const char *buf, size_t count)
{
u64 phys_addr;
- int nid;
- int ret;
+ long ret;
+
+#ifdef CONFIG_XEN_MEMORY_HOTPLUG
+ struct xen_memory_reservation reservation = {
+ .address_bits = 0,
+ .extent_order = 0,
+ .domid = DOMID_SELF,
+ .nr_extents = PAGES_PER_SECTION
+ };
+ unsigned long *frame_list, i, nr_pages, pfn;
+#endif

phys_addr = simple_strtoull(buf, NULL, 0);

- nid = memory_add_physaddr_to_nid(phys_addr);
- ret = add_memory(nid, phys_addr, PAGES_PER_SECTION << PAGE_SHIFT);
+#ifdef CONFIG_XEN_MEMORY_HOTPLUG
+ if (xen_domain()) {
+ if (!(frame_list = vmalloc(PAGES_PER_SECTION * sizeof(unsigned long)))) {
+ printk(KERN_ERR "%s: vmalloc: Out of memory\n", __func__);
+ return -ENOMEM;
+ }
+
+ set_xen_guest_handle(reservation.extent_start, frame_list);
+ for (i = 0, pfn = phys_addr >> PAGE_SHIFT; i < PAGES_PER_SECTION; ++i, ++pfn)
+ frame_list[i] = pfn;
+
+ ret = HYPERVISOR_memory_op(XENMEM_populate_physmap, &reservation);
+
+ if (ret < PAGES_PER_SECTION) {
+ if (ret > 0) {
+ printk(KERN_ERR "%s: PHYSMAP is not fully populated: %li/%lu\n",
+ __func__, ret, PAGES_PER_SECTION);
+ reservation.nr_extents = nr_pages = ret;
+ ret = HYPERVISOR_memory_op(XENMEM_decrease_reservation, &reservation);
+ BUG_ON(ret != nr_pages);
+ ret = -ENOMEM;
+ } else {
+ ret = (ret < 0) ? ret : -ENOMEM;
+ printk(KERN_ERR "%s: Can't populate PHYSMAP: %li\n", __func__, ret);
+ }
+ vfree(frame_list);
+ return ret;
+ }
+
+ for (i = 0, pfn = phys_addr >> PAGE_SHIFT; i < PAGES_PER_SECTION; ++i, ++pfn) {
+ BUG_ON(!xen_feature(XENFEAT_auto_translated_physmap) &&
+ phys_to_machine_mapping_valid(pfn));
+ set_phys_to_machine(pfn, frame_list[i]);
+ }
+
+ vfree(frame_list);
+ }
+#endif
+
+ ret = add_memory(memory_add_physaddr_to_nid(phys_addr),
+ phys_addr, PAGES_PER_SECTION << PAGE_SHIFT);

if (ret)
count = ret;
diff -Nru linux-2.6.32.16.orig/drivers/xen/Kconfig linux-2.6.32.16/drivers/xen/Kconfig
--- linux-2.6.32.16.orig/drivers/xen/Kconfig 2010-07-05 20:14:00.000000000 +0200
+++ linux-2.6.32.16/drivers/xen/Kconfig 2010-07-09 21:04:17.000000000 +0200
@@ -7,6 +7,16 @@
the system to expand the domain's memory allocation, or alternatively
return unneeded memory to the system.

+config XEN_BALLOON_MEMORY_HOTPLUG
+ bool "Xen memory balloon driver with memory hotplug support"
+ depends on EXPERIMENTAL && XEN && XEN_BALLOON && MEMORY_HOTPLUG
+ default n
+ help
+ Xen memory balloon driver with memory hotplug support 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
@@ -60,4 +70,4 @@
Create entries under /sys/hypervisor describing the Xen
hypervisor environment. When running native or in another
virtual environment, /sys/hypervisor will still be present,
- but will have no xen contents.
\ No newline at end of file
+ but will have no xen contents.
diff -Nru linux-2.6.32.16.orig/drivers/xen/balloon.c linux-2.6.32.16/drivers/xen/balloon.c
--- linux-2.6.32.16.orig/drivers/xen/balloon.c 2010-07-05 20:14:00.000000000 +0200
+++ linux-2.6.32.16/drivers/xen/balloon.c 2010-07-16 15:06:53.000000000 +0200
@@ -6,6 +6,7 @@
* 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
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License version 2
@@ -74,6 +75,10 @@
/* Number of pages in high- and low-memory balloons. */
unsigned long balloon_low;
unsigned long balloon_high;
+#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
+ u64 hotplug_start_addr;
+ u64 hotplug_size;
+#endif
};

static DEFINE_MUTEX(balloon_mutex);
@@ -183,6 +188,9 @@

static unsigned long current_target(void)
{
+#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
+ return balloon_stats.target_pages;
+#else
unsigned long target = balloon_stats.target_pages;

target = min(target,
@@ -191,6 +199,7 @@
balloon_stats.balloon_high);

return target;
+#endif
}

static int increase_reservation(unsigned long nr_pages)
@@ -204,17 +213,48 @@
.domid = DOMID_SELF
};

+#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
+ struct resource *r;
+#endif
+
if (nr_pages > ARRAY_SIZE(frame_list))
nr_pages = ARRAY_SIZE(frame_list);

spin_lock_irqsave(&balloon_lock, flags);

+#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
+ if (!balloon_stats.balloon_low && !balloon_stats.balloon_high) {
+ if (!balloon_stats.hotplug_start_addr)
+ for (r = iomem_resource.child; r; r = r->sibling)
+ if (!r->sibling || r->sibling->start >
+ (((r->end >> PAGE_SHIFT) + balloon_stats.target_pages -
+ balloon_stats.current_pages) << PAGE_SHIFT)) {
+ balloon_stats.hotplug_start_addr = (((r->end >> PAGE_SHIFT) + 1) << PAGE_SHIFT);
+ break;
+ }
+
+ pfn = (balloon_stats.hotplug_start_addr + balloon_stats.hotplug_size) >> PAGE_SHIFT;
+
+ for (i = 0; i < nr_pages; ++i, ++pfn)
+ frame_list[i] = pfn;
+
+ pfn -= nr_pages + 1;
+ } else {
+ page = balloon_first_page();
+ for (i = 0; i < nr_pages; i++) {
+ BUG_ON(page == NULL);
+ frame_list[i] = page_to_pfn(page);
+ page = balloon_next_page(page);
+ }
+ }
+#else
page = balloon_first_page();
for (i = 0; i < nr_pages; i++) {
BUG_ON(page == NULL);
frame_list[i] = page_to_pfn(page);
page = balloon_next_page(page);
}
+#endif

set_xen_guest_handle(reservation.extent_start, frame_list);
reservation.nr_extents = nr_pages;
@@ -223,15 +263,30 @@
goto out;

for (i = 0; i < rc; i++) {
+#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
+ if (balloon_stats.hotplug_start_addr)
+ ++pfn;
+ else {
+ page = balloon_retrieve();
+ BUG_ON(page == NULL);
+ pfn = page_to_pfn(page);
+ }
+#else
page = balloon_retrieve();
BUG_ON(page == NULL);
-
pfn = page_to_pfn(page);
+#endif
+
BUG_ON(!xen_feature(XENFEAT_auto_translated_physmap) &&
phys_to_machine_mapping_valid(pfn));

set_phys_to_machine(pfn, frame_list[i]);

+#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
+ if (balloon_stats.hotplug_start_addr)
+ continue;
+#endif
+
/* Link back into the page tables if not highmem. */
if (pfn < max_low_pfn) {
int ret;
@@ -248,6 +303,11 @@
__free_page(page);
}

+#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
+ if (balloon_stats.hotplug_start_addr)
+ balloon_stats.hotplug_size += rc << PAGE_SHIFT;
+#endif
+
balloon_stats.current_pages += rc;

out:
@@ -344,8 +404,24 @@
} while ((credit != 0) && !need_sleep);

/* Schedule more work if there is some still to be done. */
+
+#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
if (current_target() != balloon_stats.current_pages)
mod_timer(&balloon_timer, jiffies + HZ);
+ else
+ if (balloon_stats.hotplug_start_addr) {
+ /* TODO: deallocate memory if something goes wrong !!! */
+ add_memory(memory_add_physaddr_to_nid(balloon_stats.hotplug_start_addr),
+ balloon_stats.hotplug_start_addr, balloon_stats.hotplug_size);
+ online_pages(balloon_stats.hotplug_start_addr >> PAGE_SHIFT,
+ balloon_stats.hotplug_size >> PAGE_SHIFT);
+ balloon_stats.hotplug_start_addr = 0;
+ balloon_stats.hotplug_size = 0;
+ }
+#else
+ if (current_target() != balloon_stats.current_pages)
+ mod_timer(&balloon_timer, jiffies + HZ);
+#endif

mutex_unlock(&balloon_mutex);
}
@@ -413,6 +489,11 @@
balloon_stats.balloon_high = 0;
balloon_stats.driver_pages = 0UL;

+#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
+ balloon_stats.hotplug_start_addr = 0;
+ balloon_stats.hotplug_size = 0;
+#endif
+
init_timer(&balloon_timer);
balloon_timer.data = 0;
balloon_timer.function = balloon_alarm;
diff -Nru linux-2.6.32.16.orig/mm/Kconfig linux-2.6.32.16/mm/Kconfig
--- linux-2.6.32.16.orig/mm/Kconfig 2010-07-05 20:14:00.000000000 +0200
+++ linux-2.6.32.16/mm/Kconfig 2010-07-16 11:44:27.000000000 +0200
@@ -140,6 +140,15 @@
depends on MEMORY_HOTPLUG && ARCH_ENABLE_MEMORY_HOTREMOVE
depends on MIGRATION

+config XEN_MEMORY_HOTPLUG
+ bool "Allow for memory hot-add in Xen guests"
+ depends on EXPERIMENTAL && ARCH_MEMORY_PROBE && XEN
+ default n
+ help
+ Memory hot-add 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.
+
#
# If we have space for more page flags then we can enable additional
# optimizations and functionality.
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