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Subject[PATCH v3] memory-hotplug: add automatic onlining policy for the newly added memory
Date
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@lwn.net>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Daniel Kiper <daniel.kiper@oracle.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Tang Chen <tangchen@cn.fujitsu.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Xishi Qiu <qiuxishi@huawei.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: "K. Y. Srinivasan" <kys@microsoft.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Kay Sievers <kay@vrfy.org>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
- 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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