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[PATCH v5 2/2] xen_balloon: support memory auto onlining policy

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  [PATCH v5 2/2] xen_balloon: support memory auto onlining policy Vitaly Kuznetsov <vkuznets@redhat.com> - 2016-01-13 18:40 +0100
    Re: [PATCH v5 2/2] xen_balloon: support memory auto onlining policy Daniel Kiper <daniel.kiper@oracle.com> - 2016-01-13 21:50 +0100
    Re: [PATCH v5 2/2] xen_balloon: support memory auto onlining policy David Vrabel <david.vrabel@citrix.com> - 2016-01-14 11:30 +0100

#1308664 — [PATCH v5 2/2] xen_balloon: support memory auto onlining policy

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

Suggested-by: Daniel Kiper <daniel.kiper@oracle.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
Changes since v4:
- 'dom0' -> 'control domain', 'domU' -> 'target domain' in Kconfig
  [David Vrabel]
- always call add_memory_resource() with memhp_auto_online [David Vrabel]
---
 drivers/xen/Kconfig   | 20 +++++++++++++-------
 drivers/xen/balloon.c | 11 ++++++++++-
 2 files changed, 23 insertions(+), 8 deletions(-)

diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
index 73708ac..addcb7f 100644
--- a/drivers/xen/Kconfig
+++ b/drivers/xen/Kconfig
@@ -37,23 +37,29 @@ 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,
 
-	    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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#1308796

On Wed, Jan 13, 2016 at 06:32:30PM +0100, Vitaly Kuznetsov wrote:
> Add support for the newly added kernel memory auto onlining policy to Xen
> ballon driver.
>
> Suggested-by: Daniel Kiper <daniel.kiper@oracle.com>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>

In general Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
but one nitpick below...

Thank you for doing this work.

> ---
> Changes since v4:
> - 'dom0' -> 'control domain', 'domU' -> 'target domain' in Kconfig
>   [David Vrabel]
> - always call add_memory_resource() with memhp_auto_online [David Vrabel]
> ---
>  drivers/xen/Kconfig   | 20 +++++++++++++-------
>  drivers/xen/balloon.c | 11 ++++++++++-
>  2 files changed, 23 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
> index 73708ac..addcb7f 100644
> --- a/drivers/xen/Kconfig
> +++ b/drivers/xen/Kconfig
> @@ -37,23 +37,29 @@ 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,

Please change "dumU" to "target domain".

Daniel

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#1309156

On 13/01/16 17:32, Vitaly Kuznetsov wrote:
> Add support for the newly added kernel memory auto onlining policy to Xen
> ballon driver.

Acked-by: David Vrabel <david.vrabel@citrix.com>

Thanks.

David

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