Currently, all newly added memory blocks remain in 'offline' state unless
someone onlines them, some linux distributions carry special udev rules
like:
SUBSYSTEM=="memory", ACTION=="add", ATTR{state}=="offline", ATTR{state}="online"
to make this happen automatically. This is not a great solution for virtual
machines where memory hotplug is being used to address high memory pressure
situations as such onlining is slow and a userspace process doing this
(udev) has a chance of being killed by the OOM killer as it will probably
require to allocate some memory.
Introduce default policy for the newly added memory blocks in
/sys/devices/system/memory/auto_online_blocks file with two possible
values: "offline" which preserves the current behavior and "online" which
causes all newly added memory blocks to go online as soon as they're added.
The default is "offline".
Signed-off-by: Vitaly Kuznetsov
---
Changes since v4:
- Use memory_block_change_state() through walk_memory_range() instead of
online_pages() to correctly handle possible failures [David Rientjes]
- Minor memory-hotplug.txt changes (keep the old title, explicitly word
that we have a global policy here) [David Rientjes, Daniel Kiper]
---
Documentation/memory-hotplug.txt | 20 +---
drivers/base/memory.c| 34 +-
drivers/xen/balloon.c| 2 +-
include/linux/memory.h | 3 +++
include/linux/memory_hotplug.h | 4 +++-
mm/memory_hotplug.c | 17 +++--
6 files changed, 72 insertions(+), 8 deletions(-)
diff --git a/Documentation/memory-hotplug.txt b/Documentation/memory-hotplug.txt
index ce2cfcf..b259c6c 100644
--- a/Documentation/memory-hotplug.txt
+++ b/Documentation/memory-hotplug.txt
@@ -256,10 +256,24 @@ If the memory block is offline, you'll read "offline".
5.2. How to online memory
-Even if the memory is hot-added, it is not at ready-to-use state.
-For using newly added memory, you have to "online" the memory block.
+When the memory is hot-added, the kernel decides whether or not to "online"
+it according to the policy which can be read from "auto_online_blocks" file:
-For onlining, you have to write "online" to the memory block's state file as:
+% cat /sys/devices/system/memory/auto_online_blocks
+
+The default is "offline" which means the newly added memory is not in a
+ready-to-use state and you have to "online" the newly added memory blocks
+manually. Automatic onlining can be requested by writing "online" to
+"auto_online_blocks" file:
+
+% echo online > /sys/devices/system/memory/auto_online_blocks
+
+This sets a global policy and impacts all memory blocks that will subsequently
+be hotplugged. Currently offline blocks keep their state.
+
+If the automatic onlining wasn't requested or some memory block was offlined
+it is possible to change the individual block's state by writing to the "state"
+file:
% echo online > /sys/devices/system/memory/memoryXXX/state
diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index 25425d3..4fc240e 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -251,7 +251,7 @@ memory_block_action(unsigned long phys_index, unsigned long
action, int online_t
return ret;
}
-static int memory_block_change_state(struct memory_block *mem,
+int memory_block_change_state(struct memory_block *mem,
unsigned long to_state, unsigned long from_state_req)
{
int ret = 0;
@@ -439,6 +439,37 @@ print_block_size(struct device *dev, struct
device_attribute *attr,
static DEVICE_ATTR(block_size_bytes, 0444, print_block_size, NULL);
/*
+ * Memory auto online policy.
+ */
+
+static ssize_t
+show_auto_online_blocks(struct device *dev, struct device_attribute *attr,
+ char *buf)
+{
+ if (memhp_auto_online)
+ return sprintf(buf, "online\n");
+ else
+ return sprintf(buf, "offline\n");
+}
+
+static ssize_t
+store_auto_online_blocks(struct device *dev, struct device_attribute *attr,
+const char *buf, size_t count)
+{
+ if (sysfs_streq(buf, "online"))
+ memhp_auto_online = true;
+ else if (sysfs_streq(buf, "offline"))
+ memhp_auto_online = false;
+ else
+ return -EINVAL;
+
+ return count;
+}
+
+static DEVICE_ATTR(auto_online_blocks, 0644, show_auto_online_blocks,
+ store_auto_online_blocks);
+
+/*
* Some architectures will have custom drivers to do this, and
* will not need to do it from userspace. The fake hot-add code
* as well as ppc64 will do all of their discovery in userspace
@@ -737,6 +768,7 @@ static struct attribute *memory_root_attrs[] = {
#endif
&dev_attr_block_size_bytes.attr,
+ &dev_attr_auto_online_blocks.attr,
NULL
};
diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index 12eab50..890c3b5 100644
--- a/drivers/xen/balloon.c
+++ b/
