linux-kernel - [RFC] hotplug, memory: move register_memory_resource out of the lock_memory

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Date:	Tue, 14 Jan 2014 12:24:34 -0600
From:	Nathan Zimmer <nzimmer@....com>
To:	unlisted-recipients:; (no To-header on input)
Cc:	Nathan Zimmer <nzimmer@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tang Chen <tangchen@...fujitsu.com>,
	Wen Congyang <wency@...fujitsu.com>,
	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Hedi <hedi@....com>, Mike Travis <travis@....com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: [RFC] hotplug, memory: move register_memory_resource out of the lock_memory_hotplug

We don't need to do register_memory_resource() since it has its own lock and
doesn't make any callbacks.

Also register_memory_resource return NULL on failure so we don't have anything
to cleanup at this point.

The reason for this rfc is I was doing some experiments with hotplugging of
memory on some of our larger systems.  While it seems to work, it can be quite
slow.  With some preliminary digging I found that lock_memory_hotplug is
clearly ripe for breakup.

It could be broken up per nid or something but it also covers the
online_page_callback.  The online_page_callback shouldn't be very hard to break
out.

Also there is the issue of various structures(wmarks come to mind) that are
only updated under the lock_memory_hotplug that would need to be dealt with.

cc: Andrew Morton <akpm@...ux-foundation.org>
cc: Tang Chen <tangchen@...fujitsu.com>
cc: Wen Congyang <wency@...fujitsu.com>
cc: Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
cc: Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
cc: "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
cc: Hedi <hedi@....com>
cc: Mike Travis <travis@....com>
cc: linux-mm@...ck.org
cc: linux-kernel@...r.kernel.org

---
 mm/memory_hotplug.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 1ad92b4..62a0cd1 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1097,17 +1097,18 @@ int __ref add_memory(int nid, u64 start, u64 size)
 	struct resource *res;
 	int ret;

-	lock_memory_hotplug();
-
 	res = register_memory_resource(start, size);
 	ret = -EEXIST;
 	if (!res)
-		goto out;
+		return ret;

 	{	/* Stupid hack to suppress address-never-null warning */
 		void *p = NODE_DATA(nid);
 		new_pgdat = !p;
 	}
+
+	lock_memory_hotplug();
+
 	new_node = !node_online(nid);
 	if (new_node) {
 		pgdat = hotadd_new_pgdat(nid, start);
-- 
1.8.2.1

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