[Xen-devel] [PATCH v6 2/2] xen_balloon: support memory auto onlining policy

[Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>]

Add support for the newly added kernel memory auto onlining policy to Xen
ballon driver.

Suggested-by: Daniel Kiper <daniel.kiper@xxxxxxxxxx>
Reviewed-by: Daniel Kiper <daniel.kiper@xxxxxxxxxx>
Acked-by: David Vrabel <david.vrabel@xxxxxxxxxx>
Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
---
Changes since v5:
- Change the last 'domU' -> 'target domain' in Kconfig [Daniel Kiper]
---
 drivers/xen/Kconfig   | 23 +++++++++++++++--------
 drivers/xen/balloon.c | 11 ++++++++++-
 2 files changed, 25 insertions(+), 9 deletions(-)

diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
index 73708ac..979a8317 100644
--- a/drivers/xen/Kconfig
+++ b/drivers/xen/Kconfig
@@ -37,23 +37,30 @@ config XEN_BALLOON_MEMORY_HOTPLUG
 
          Memory could be hotplugged in following steps:
 
-           1) dom0: xl mem-max <domU> <maxmem>
+           1) target domain: ensure that memory auto online policy is in
+              effect by checking /sys/devices/system/memory/auto_online_blocks
+              file (should be 'online').
+
+           2) control domain: xl mem-max <target-domain> <maxmem>
               where <maxmem> is >= requested memory size,
 
-           2) dom0: xl mem-set <domU> <memory>
+           3) control domain: xl mem-set <target-domain> <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,
+              /sys/devices/system/xen_memory/xen_memory0/target_kb on the
+              target domain.
 
-           3) domU: for i in /sys/devices/system/memory/memory*/state; do \
-                      [ "`cat "$i"`" = offline ] && echo online > "$i"; done
+         Alternatively, if memory auto onlining was not requested at step 1
+         the newly added memory can be manually onlined in the target domain
+         by doing the following:
 
-         Memory could be onlined automatically on domU by adding following 
line to udev rules:
+               for i in /sys/devices/system/memory/memory*/state; do \
+                 [ "`cat "$i"`" = offline ] && echo online > "$i"; done
 
-         SUBSYSTEM=="memory", ACTION=="add", RUN+="/bin/sh -c '[ -f 
/sys$devpath/state ] && echo online > /sys$devpath/state'"
+         or by adding the following line to udev rules:
 
-         In that case step 3 should be omitted.
+         SUBSYSTEM=="memory", ACTION=="add", RUN+="/bin/sh -c '[ -f 
/sys$devpath/state ] && echo online > /sys$devpath/state'"
 
 config XEN_BALLOON_MEMORY_HOTPLUG_LIMIT
        int "Hotplugged memory limit (in GiB) for a PV guest"
diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index 890c3b5..f8cca0c 100644
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -338,7 +338,16 @@ static enum bp_state reserve_additional_memory(void)
        }
 #endif
 
-       rc = add_memory_resource(nid, resource, false);
+       /*
+        * add_memory_resource() will call online_pages() which in its turn
+        * will call xen_online_page() callback causing deadlock if we don't
+        * release balloon_mutex here. Unlocking here is safe because the
+        * callers drop the mutex before trying again.
+        */
+       mutex_unlock(&balloon_mutex);
+       rc = add_memory_resource(nid, resource, memhp_auto_online);
+       mutex_lock(&balloon_mutex);
+
        if (rc) {
                pr_warn("Cannot add additional memory (%i)\n", rc);
                goto err;
-- 
2.5.0


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