[PATCH v2] memory-hotplug: add automatic onlining policy for the newly added memory

* [PATCH v2] memory-hotplug: add automatic onlining policy for the newly added memory
@ 2015-12-22 16:32 ` Vitaly Kuznetsov
  0 siblings, 0 replies; 21+ messages in thread
From: Vitaly Kuznetsov @ 2015-12-22 16:32 UTC (permalink / raw)
  To: linux-mm
  Cc: linux-doc, linux-kernel, xen-devel, Jonathan Corbet,
	Greg Kroah-Hartman, Daniel Kiper, Dan Williams, Tang Chen,
	David Vrabel, David Rientjes, Andrew Morton, Naoya Horiguchi,
	Xishi Qiu, Mel Gorman, K. Y. Srinivasan, Igor Mammedov,
	Kay Sievers, Konrad Rzeszutek Wilk, Boris Ostrovsky

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/hotplug_autoonline 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 "online" when MEMORY_HOTPLUG_AUTOONLINE kernel config option
is selected.

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 '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/kernel-parameters.txt |  2 ++
 Documentation/memory-hotplug.txt    | 26 ++++++++++++++++++++------
 drivers/base/memory.c               | 36 ++++++++++++++++++++++++++++++++++++
 drivers/xen/balloon.c               |  2 +-
 include/linux/memory_hotplug.h      |  6 +++++-
 mm/Kconfig                          |  9 +++++++++
 mm/memory_hotplug.c                 | 25 +++++++++++++++++++++++--
 7 files changed, 96 insertions(+), 10 deletions(-)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 742f69d..652efe1 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2537,6 +2537,8 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			shutdown the other cpus.  Instead use the REBOOT_VECTOR
 			irq.
 
+	nomemhp_autoonline	Don't automatically online newly added memory.
+
 	nomodule	Disable module load
 
 	nopat		[X86] Disable PAT (page attribute table extension of
diff --git a/Documentation/memory-hotplug.txt b/Documentation/memory-hotplug.txt
index ce2cfcf..041efac 100644
--- a/Documentation/memory-hotplug.txt
+++ b/Documentation/memory-hotplug.txt
@@ -111,8 +111,9 @@ To use memory hotplug feature, kernel must be compiled with following
 config options.
 
 - For all memory hotplug
-    Memory model -> Sparse Memory  (CONFIG_SPARSEMEM)
-    Allow for memory hot-add       (CONFIG_MEMORY_HOTPLUG)
+    Memory model -> Sparse Memory         (CONFIG_SPARSEMEM)
+    Allow for memory hot-add              (CONFIG_MEMORY_HOTPLUG)
+    Automatically online hot-added memory (CONFIG_MEMORY_HOTPLUG_AUTOONLINE)
 
 - To enable memory removal, the followings are also necessary
     Allow for memory hot remove    (CONFIG_MEMORY_HOTREMOVE)
@@ -254,12 +255,25 @@ 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 "hotplug_autoonline" file
+(requires CONFIG_MEMORY_HOTPLUG_AUTOONLINE):
 
-For onlining, you have to write "online" to the memory block's state file as:
+% cat /sys/devices/system/memory/hotplug_autoonline
+
+The default is "online" which means the newly added memory will be onlined
+after adding. Automatic onlining can be disabled by writing "offline" to the
+"hotplug_autoonline" file:
+
+% echo offline > /sys/devices/system/memory/hotplug_autoonline
+
+or by booting the kernel with "nomemhp_autoonline" parameter.
+
+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..6f9ce3a 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -438,6 +438,39 @@ print_block_size(struct device *dev, struct device_attribute *attr,
 
 static DEVICE_ATTR(block_size_bytes, 0444, print_block_size, NULL);
 
+#ifdef CONFIG_MEMORY_HOTPLUG_AUTOONLINE
+/*
+ * Memory auto online policy.
+ */
+
+static ssize_t
+show_memhp_autoonline(struct device *dev, struct device_attribute *attr,
+		      char *buf)
+{
+	if (memhp_autoonline)
+		return sprintf(buf, "online\n");
+	else
+		return sprintf(buf, "offline\n");
+}
+
+static ssize_t
+store_memhp_autoonline(struct device *dev, struct device_attribute *attr,
+		       const char *buf, size_t count)
+{
+	if (sysfs_streq(buf, "online"))
+		memhp_autoonline = true;
+	else if (sysfs_streq(buf, "offline"))
+		memhp_autoonline = false;
+	else
+		return -EINVAL;
+
+	return count;
+}
+
+static DEVICE_ATTR(hotplug_autoonline, 0644, show_memhp_autoonline,
+		   store_memhp_autoonline);
+#endif
+
 /*
  * Some architectures will have custom drivers to do this, and
  * will not need to do it from userspace.  The fake hot-add code
@@ -737,6 +770,9 @@ static struct attribute *memory_root_attrs[] = {
 #endif
 
 	&dev_attr_block_size_bytes.attr,
+#ifdef CONFIG_MEMORY_HOTPLUG_AUTOONLINE
+	&dev_attr_hotplug_autoonline.attr,
+#endif
 	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..367e7d2 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -99,6 +99,10 @@ extern void __online_page_free(struct page *page);
 
 extern int try_online_node(int nid);
 
+#ifdef CONFIG_MEMORY_HOTPLUG_AUTOONLINE
+extern bool memhp_autoonline;
+#endif
+
 #ifdef CONFIG_MEMORY_HOTREMOVE
 extern bool is_pageblock_removable_nolock(struct page *page);
 extern int arch_remove_memory(u64 start, u64 size);
@@ -267,7 +271,7 @@ 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/Kconfig b/mm/Kconfig
index 97a4e06..dd1b8ea 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -200,6 +200,15 @@ config MEMORY_HOTREMOVE
 	depends on MEMORY_HOTPLUG && ARCH_ENABLE_MEMORY_HOTREMOVE
 	depends on MIGRATION
 
+config MEMORY_HOTPLUG_AUTOONLINE
+	bool "Automatically online hot-added memory"
+	depends on MEMORY_HOTPLUG_SPARSE
+	help
+	  When memory is hot-added, it is not at ready-to-use state, a special
+	  userspace action is required to online the newly added blocks. With
+	  this option enabled, the kernel will try to online all newly added
+	  memory automatically.
+
 # Heavily threaded applications may benefit from splitting the mm-wide
 # page_table_lock, so that faults on different parts of the user address
 # space can be handled with less contention: split it at this NR_CPUS.
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 67d488a..32a7b7c 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -76,6 +76,18 @@ static struct {
 #define memhp_lock_acquire()      lock_map_acquire(&mem_hotplug.dep_map)
 #define memhp_lock_release()      lock_map_release(&mem_hotplug.dep_map)
 
+#ifdef CONFIG_MEMORY_HOTPLUG_AUTOONLINE
+bool memhp_autoonline = true;
+EXPORT_SYMBOL_GPL(memhp_autoonline);
+
+static int __init setup_memhp_autoonline(char *str)
+{
+	memhp_autoonline = false;
+	return 0;
+}
+__setup("nomemhp_autoonline", setup_memhp_autoonline);
+#endif
+
 void get_online_mems(void)
 {
 	might_sleep();
@@ -1232,7 +1244,7 @@ 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 +1304,11 @@ 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 +1332,11 @@ int __ref add_memory(int nid, u64 start, u64 size)
 	if (!res)
 		return -EEXIST;
 
-	ret = add_memory_resource(nid, res);
+#ifdef CONFIG_MEMORY_HOTPLUG_AUTOONLINE
+	ret = add_memory_resource(nid, res, memhp_autoonline);
+#else
+	ret = add_memory_resource(nid, res, false);
+#endif
 	if (ret < 0)
 		release_memory_resource(res);
 	return ret;
-- 
2.4.3


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