memory-hotplug: add automatic onlining policy for the newly added memory

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 <vkuznets@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
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>
Acked-by: David Rientjes <rientjes@google.com>
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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 15 insertions, 2 deletions

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 979b18cbd343..484e86761b3e 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -77,6 +77,9 @@ 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();
@@ -1261,8 +1264,13 @@ int zone_for_memory(int nid, u64 start, u64 size, int zone_default,
         return zone_default;
 }
 
+static int online_memory_block(struct memory_block *mem, void *arg)
+{
+        return memory_block_change_state(mem, MEM_ONLINE, MEM_OFFLINE);
+}
+
 /* 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;
@@ -1322,6 +1330,11 @@ 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)
+                walk_memory_range(PFN_DOWN(start), PFN_UP(start + size - 1),
+                                  NULL, online_memory_block);
+
         goto out;
 
 error:
@@ -1345,7 +1358,7 @@ int __ref add_memory(int nid, u64 start, u64 size)
         if (IS_ERR(res))
                 return PTR_ERR(res);
 
-        ret = add_memory_resource(nid, res);
+        ret = add_memory_resource(nid, res, memhp_auto_online);
         if (ret < 0)
                 release_memory_resource(res);
         return ret;