xen/balloon: memory hotplug support for Xen balloon driver

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.

Memory could be hotplugged in following steps:

  1) dom0: xl mem-max <domU> <maxmem>
     where <maxmem> is >= requested memory size,

  2) dom0: xl mem-set <domU> <memory>
     where <memory> is requested memory size; alternatively memory
     could be added by writing proper value to
     /sys/devices/system/xen_memory/xen_memory0/target or
     /sys/devices/system/xen_memory/xen_memory0/target_kb on dumU,

  3) domU: for i in /sys/devices/system/memory/memory*/state; do \
             [ "`cat "$i"`" = offline ] && echo online > "$i"; done

Memory could be onlined automatically on domU by adding following line to
udev rules:

  SUBSYSTEM=="memory", ACTION=="add", RUN+="/bin/sh -c '[ -f /sys$devpath/state ] && echo online > /sys$devpath/state'"

In that case step 3 should be omitted.

Signed-off-by: Daniel Kiper <dkiper@net-space.pl>
Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Ian Campbell <ian.campbell@citrix.com>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 30 insertions, 0 deletions

diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
index 03bc471c3eed..f815283667af 100644
--- a/drivers/xen/Kconfig
+++ b/drivers/xen/Kconfig
@@ -26,6 +26,36 @@ config XEN_SELFBALLOONING
 	  kernel boot parameter.  Note that systems without a sufficiently
 	  large swap device should not enable self-ballooning.
 
+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.
+
+	  Memory could be hotplugged in following steps:
+
+	    1) dom0: xl mem-max <domU> <maxmem>
+	       where <maxmem> is >= requested memory size,
+
+	    2) dom0: xl mem-set <domU> <memory>
+	       where <memory> is requested memory size; alternatively memory
+	       could be added by writing proper value to
+	       /sys/devices/system/xen_memory/xen_memory0/target or
+	       /sys/devices/system/xen_memory/xen_memory0/target_kb on dumU,
+
+	    3) domU: for i in /sys/devices/system/memory/memory*/state; do \
+	               [ "`cat "$i"`" = offline ] && echo online > "$i"; done
+
+	  Memory could be onlined automatically on domU by adding following line to udev rules:
+
+	  SUBSYSTEM=="memory", ACTION=="add", RUN+="/bin/sh -c '[ -f /sys$devpath/state ] && echo online > /sys$devpath/state'"
+
+	  In that case step 3 should be omitted.
+
 config XEN_SCRUB_PAGES
 	bool "Scrub pages before returning them to system"
 	depends on XEN_BALLOON