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".
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Daniel Kiper <daniel.kiper@xxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Tang Chen <tangchen@xxxxxxxxxxxxxx>
Cc: David Vrabel <david.vrabel@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Cc: Xishi Qiu <qiuxishi@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx>
Cc: Igor Mammedov <imammedo@xxxxxxxxxx>
Cc: Kay Sievers <kay@xxxxxxxx>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
---
- Changes since 'v2':
- Remove config option, revert to 'offline' by default [Andrew Morton,
David Rientjes]
- Rename 'hotplug_autoonline' to 'auto_online_blocks' [David Rientjes]
- Changes since 'v1':
Add 'online' parameter to add_memory_resource() as it is being used by
xen ballon driver and it adds "empty" memory pages [David Vrabel].
(I don't completely understand what prevents manual onlining in this
case as we still have all newly added blocks in sysfs ... this is the
discussion point.)
- Changes since 'RFC':
It seems nobody is strongly opposed to the idea, thus non-RFC.
Change memhp_autoonline to bool, we support only MMOP_ONLINE_KEEP
and MMOP_OFFLINE for the auto-onlining policy, eliminate 'unknown'
from show_memhp_autoonline(). [Daniel Kiper]
Put everything under CONFIG_MEMORY_HOTPLUG_AUTOONLINE, enable the
feature by default (when the config option is selected) and add
kernel parameter (nomemhp_autoonline) to disable the functionality
upon boot when needed.
- RFC:
I was able to find previous attempts to fix the issue, e.g.:
http://marc.info/?l=linux-kernel&m=137425951924598&w=2
http://marc.info/?l=linux-acpi&m=127186488905382
but I'm not completely sure why it didn't work out and the solution
I suggest is not 'smart enough', thus 'RFC'.
---
Documentation/memory-hotplug.txt | 19 +++++++++++++++----
drivers/base/memory.c | 32 ++++++++++++++++++++++++++++++++
drivers/xen/balloon.c | 2 +-
include/linux/memory_hotplug.h | 4 +++-
mm/memory_hotplug.c | 12 ++++++++++--
5 files changed, 61 insertions(+), 8 deletions(-)
diff --git a/Documentation/memory-hotplug.txt b/Documentation/memory-hotplug.txt
index ce2cfcf..ceaf40c 100644
--- a/Documentation/memory-hotplug.txt
+++ b/Documentation/memory-hotplug.txt
@@ -254,12 +254,23 @@ If the memory block is online, you'll read "online".
If the memory block is offline, you'll read "offline".
-5.2. How to online memory
+5.2. Memory onlining
------------
-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
+
+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..44a618d 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -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/drivers/xen/balloon.c
@@ -338,7 +338,7 @@ static enum bp_state reserve_additional_memory(void)
}
#endif
- rc = add_memory_resource(nid, resource);
+ rc = add_memory_resource(nid, resource, false);
if (rc) {
pr_warn("Cannot add additional memory (%i)\n", rc);
goto err;
diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index 2ea574f..4b7949a 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -99,6 +99,8 @@ extern void __online_page_free(struct page *page);
extern int try_online_node(int nid);
+extern bool memhp_auto_online;
+
#ifdef CONFIG_MEMORY_HOTREMOVE
extern bool is_pageblock_removable_nolock(struct page *page);
extern int arch_remove_memory(u64 start, u64 size);
@@ -267,7 +269,7 @@ static inline void remove_memory(int nid, u64 start, u64 size) {}
extern int walk_memory_range(unsigned long start_pfn, unsigned long end_pfn,
void *arg, int (*func)(struct memory_block *, void *));
extern int add_memory(int nid, u64 start, u64 size);
-extern int add_memory_resource(int nid, struct resource *resource);
+extern int add_memory_resource(int nid, struct resource *resource, bool online);
extern int zone_for_memory(int nid, u64 start, u64 size, int zone_default,
bool for_device);
extern int arch_add_memory(int nid, u64 start, u64 size, bool for_device);
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index a042a9d..0ecf860 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -76,6 +76,9 @@ static struct {
#define memhp_lock_acquire() lock_map_acquire(&mem_hotplug.dep_map)
#define memhp_lock_release() lock_map_release(&mem_hotplug.dep_map)
+bool memhp_auto_online;
+EXPORT_SYMBOL_GPL(memhp_auto_online);
+
void get_online_mems(void)
{
might_sleep();
@@ -1232,7 +1235,7 @@ int zone_for_memory(int nid, u64 start, u64 size, int zone_default,
}
/* we are OK calling __meminit stuff here - we have CONFIG_MEMORY_HOTPLUG */
-int __ref add_memory_resource(int nid, struct resource *res)
+int __ref add_memory_resource(int nid, struct resource *res, bool online)
{
u64 start, size;
pg_data_t *pgdat = NULL;
@@ -1292,6 +1295,11 @@ int __ref add_memory_resource(int nid, struct resource *res)
/* create new memmap entry */
firmware_map_add_hotplug(start, start + size, "System RAM");
+ /* online pages if requested */
+ if (online)
+ online_pages(start >> PAGE_SHIFT, size >> PAGE_SHIFT,
+ MMOP_ONLINE_KEEP);
+
goto out;
error:
@@ -1315,7 +1323,7 @@ int __ref add_memory(int nid, u64 start, u64 size)
if (!res)
return -EEXIST;
- ret = add_memory_resource(nid, res);
+ ret = add_memory_resource(nid, res, memhp_auto_online);
if (ret < 0)
release_memory_resource(res);
return ret;
--
2.4.3
--
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